Filed Pursuant to Rule 424(b)(5)
Registration Numbers: 333-210248

PROSPECTUS SUPPLEMENT

(to Prospectus Dated April 28, 2016)

1,105,263 Shares

Common Stock

We are offering 1,105,263 shares of our common stock.

Our common stock trades on The NASDAQ Capital Market under the symbol “CBIO.” On December 18, 2017, the last reported sale price of the common stock on The NASDAQ Capital Market was $10.57 per share.

As of December 18, 2017, the aggregate market value of our outstanding common stock held by non-affiliates, or the public float, was approximately $48.1 million based on 4,708,517 shares of outstanding stock, of which 4,545,624 are held by non-affiliates, and a per share price of $10.57, which was the closing sale price of our common stock on December 18, 2017. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell our common stock in a public primary offering with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75,000,000. We have offered approximately $5.5 million securities pursuant to General Instruction I.B.6 of Form S-3 during the prior 12 calendar month period that ends on and includes the date of this prospectus supplement. As of December 18, 2017, one-third of our public float is equal to approximately $16.0 million.

INVESTING IN OUR SECURITIES INVOLVES A HIGH DEGREE OF RISK. YOU SHOULD CAREFULLY READ AND CONSIDER THE RISK FACTORS DESCRIBED IN THIS PROSPECTUS SUPPLEMENT, THE ACCOMPANYING BASE PROSPECTUS AND IN THE DOCUMENTS INCORPORATED BY REFERENCE INTO THIS PROSPECTUS SUPPLEMENT. SEE “RISK FACTORS” BEGINNING ON PAGE S-5.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the shares of common stock is expected to be made on or about December 22, 2017.

Book-Running Managers

Co-Managers

LifeSci Capital

The date of this prospectus supplement is December 20, 2017

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

ABOUT THIS PROSPECTUS SUPPLEMENT

This prospectus supplement is a supplement to the accompanying base prospectus dated March 16, 2016 that is also a part of this document. This prospectus supplement and the accompanying base prospectus are part of a registration statement that we have filed with the Securities and Exchange Commission, or SEC, utilizing a “shelf” registration process. Under the shelf registration process, from time to time, we may sell any of the securities described in the accompanying base prospectus in one or more offerings. In this prospectus supplement, we provide you with specific information about this offering. This prospectus supplement, the accompanying base prospectus and the documents incorporated by reference herein and therein include important information about us, our common stock and other information you should know before investing in our common stock. This prospectus supplement also adds, updates and changes information contained in the accompanying base prospectus. You should read both this prospectus supplement and the accompanying base prospectus as well as the additional information described in this prospectus supplement under the headings “Where You Can Find More Information” and “Incorporation of Certain Documents by Reference” before investing in our common stock. To the extent that any statement that we make in this prospectus supplement is inconsistent with the statements made in the accompanying base prospectus or in any document incorporated by reference that was filed with the SEC before the date of this prospectus supplement, the statements made in the accompanying base prospectus, or such an earlier filing, as applicable, are deemed modified or superseded by the statements made in this prospectus supplement. If any statement in one of these documents is inconsistent with a statement in another document having a later date—for example, a document incorporated by reference in the accompanying base prospectus—the statement having the later date modifies or supersedes the earlier statement.

You should rely only on the information contained or incorporated by reference in this prospectus supplement, in the accompanying base prospectus, in any other prospectus supplement and in any free writing prospectus filed by us with the SEC. We have not, and the underwriters have not, authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the underwriters are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information appearing in this prospectus supplement, the accompanying base prospectus and the documents incorporated by reference is accurate only as of each of their respective dates. Our business, financial condition, results of operations and prospects may have changed since those dates. To the extent that any statement that we make in this prospectus supplement differs from or is inconsistent with statements made in the accompanying base prospectus or any documents incorporated by reference therein, the statements made in this prospectus supplement will be deemed to modify or supersede those made in the accompanying base prospectus and such documents incorporated by reference therein.

We are offering to sell, and seeking offers to buy, shares of common stock only in jurisdictions where offers and sales are permitted. The distribution of this prospectus and the offering of the common stock in certain jurisdictions may be restricted by law. Persons outside the United States who come into possession of this prospectus must inform themselves about, and observe any restrictions relating to, the offering of the common stock and the distribution of this prospectus outside the United States. This prospectus does not constitute, and may not be used in connection with, an offer to sell, or a solicitation of an offer to buy, any securities offered by this prospectus by any person in any jurisdiction in which it is unlawful for such person to make such an offer or solicitation.

For purposes of this prospectus, references to the terms “Catalyst,” “the Company,” “we,” “us” and “our” refer to Catalyst Biosciences, Inc., unless the context otherwise requires.

This prospectus and the information incorporated by reference herein and therein include trademarks, service marks and trade names owned by us or other companies. All trademarks, service marks and trade names included or incorporated by reference into this prospectus are the property of their respective owners.

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RISK FACTORS

Investing in our securities involves a high degree of risk. You should carefully consider the specific risks described below and the risks described in our Annual Report on Form 10-K for the year ended December 31, 2016 and our Quarterly Reports on Form 10-Q for the quarters ended March 31, 2017, June 30, 2017 and December 31, 2017, which are incorporated by reference in this prospectus in their entirety, as well as the other information contained in this prospectus supplement, the accompanying base prospectus and the other documents incorporated by reference, before making an investment decision. See the sections of this prospectus supplement entitled “Where You Can Find More Information” and “Incorporation of Certain Information By Reference.” Any of the risks we describe below or in the information incorporated herein by reference and in the accompanying base prospectus could cause our business, financial condition or operating results to suffer. The market price of our common stock could decline if one or more of these risks and uncertainties develop into actual events. You could lose all or part of your investment.

A substantial number of shares may be sold in the market following this offering, which may depress the market price for our common stock.

Sales of a substantial number of shares of our common stock in the public market following this offering could cause the market price of our common stock to decline. Upon completion of this offering, based on our shares outstanding as of September 30, 2017, we will have outstanding an aggregate of 5,415,824 shares of common stock, assuming no exercise of outstanding options and warrants and no conversion of our redeemable convertible notes. A substantial majority of the outstanding shares of our common stock are, and all of the shares sold in this offering upon issuance will be, freely tradable without restriction or further registration under the Securities Act of 1933, as amended, or the Securities Act, unless these shares are owned or purchased by “affiliates” as that term is defined in Rule 144 under the Securities Act. In addition, we have also registered all of the shares of common stock that we may issue under our outstanding stock options and employee stock incentive plans, and as of September 30, 2017, 771,995 shares of common stock were issuable upon the exercise of outstanding stock options at a weighted average exercise price of $14.30 per share, 404,632 additional shares of common stock were reserved for issuance under our stock option plan, 2,053,114 shares of common stock were issuable upon the exercise of outstanding warrants at a weighted exercise price of $6.32 per share, and 39,814 shares of common stock issuable upon conversion of redeemable convertible notes at a rate of $137.85 per share. As a result, these shares can be freely sold in the public market upon issuance, subject to restrictions under the securities laws.

Management will have broad discretion as to the use of proceeds from this offering and we may use the net proceeds in ways with which you may disagree.

We intend to use the net proceeds of this offering for general corporate purposes, which may include clinical trials, research and development activities, capital expenditures, facilities expansion and working capital needs. Our management will have broad discretion in the application of the net proceeds from this offering and could spend the proceeds in ways that do not improve our results of operations or enhance the value of our common stock. Accordingly, you will be relying on the judgment of our management with regard to the use of net proceeds, and you will not have the opportunity, as part of your investment decision, to assess whether the proceeds are being used appropriately. Our failure to apply these funds effectively could have a material adverse effect on our business, delay the development of our product candidates and cause the price of our common stock to decline.

You may experience future dilution as a result of this offering, future equity offerings or other equity issuances.

If you invest in our common stock, your interest may be diluted. Dilution per share to new investors in this offering represents the amount, if any, by which the price per share paid by purchasers for our common stock in

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this offering exceeds the net tangible book value per share of our common stock following the issuance of stock in this offering, any future equity offering or any other equity issuances. After giving effect to the sale of shares of common stock offered by this prospectus supplement at a public offering price of $9.50 per share, and after deducting commissions and estimated aggregate offering expenses payable by us, our as adjusted net tangible book value as of September 30, 2017 would have been approximately $34.5 million, or approximately $5.93 per share. As a result, new investors would not experience dilution from this offering.

In addition, in order to raise additional capital, we may in the future offer and issue additional shares of our common stock or other securities convertible into or exchangeable for our common stock. We cannot assure you that we will be able to sell shares or other securities in any other offering at a price per share that is equal to or greater than the price per share paid by investors in this offering, and investors purchasing shares or other securities in the future could have rights superior to existing stockholders. The price per share at which we sell additional shares of our common stock or other securities convertible into or exchangeable for our common stock in future transactions may be higher or lower than the price per share in this offering. For example, as of September 30, 2017, an aggregate of 404,632 shares of common stock were reserved and available for future grant under our option plan. Also as of such date, options to purchase 771,995 shares of our common stock were outstanding. You may incur dilution upon the grant of any shares pursuant to such plan, upon vesting of any stock awards under any such plan, or upon exercise of any such outstanding options.

We do not anticipate paying dividends on our common stock in the foreseeable future.

We currently plan to invest all available funds, including the proceeds from this offering, and future earnings, if any, in the development and growth of our business. We currently do not anticipate paying any cash dividends on our common stock in the foreseeable future. As a result, a rise in the market price of our common stock, which is uncertain and unpredictable, will be your sole source of potential gain in the foreseeable future, and you should not rely on an investment in our common stock for dividend income.

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CAUTIONARY NOTE REGARDING FORWARD LOOKING INFORMATION

This prospectus supplement and the accompanying base prospectus and the documents we incorporate by reference in this prospectus supplement and the accompanying base prospectus contain forward-looking statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934, as amended, or the Exchange Act. All statements, other than statements of historical facts, included or incorporated in this prospectus supplement and the accompanying base prospectus regarding our strategy, future operations, financial position, future revenues, projected costs, prospects, plans and objectives of management are forward-looking statements. We may, in some cases, use words such as “believes,” “expects,” “may,” “will,” “should,” “seeks,” “intends,” “plans,” “pro forma,” “estimates,” or “anticipates” or the negative of these words and phrases or other variations of these words and phrases or comparable terminology, although not all forward-looking statements contain these identifying words. These statements are based on assumptions and assessments made by our management in light of its experience and its perception of historical trends, current conditions, expected future developments and other factors our management believes to be appropriate. These forward-looking statements are subject to a number of risks and uncertainties, including those risks described or incorporated by reference in this prospectus supplement and the accompanying base prospectus under “Risk Factors.”

Forward-looking statements included or incorporated by reference in this prospectus include, for example, statements about:

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Any such forward-looking statements are not guarantees of future performance and actual results, developments and business decisions may differ from those contemplated by such forward-looking statements. All such forward looking statements are made only as of the date of the document in which they are contained, based on information available to us as of the date of that document, and we caution you not to place undue reliance on forward looking statements in light of the risks and uncertainties associated with them. We disclaim any duty to update any forward-looking statements. You should also carefully consider other information set forth in reports or other documents that we file with the SEC.

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USE OF PROCEEDS

We expect the net proceeds from this offering to be approximately $        million, based on the public offering price of $        per share, after deducting underwriting discounts and commissions and estimated offering expenses payable by us. We intend to use the net proceeds from the sale of the shares of common stock under this prospectus supplement for general corporate purposes, which may include clinical trials, research and development activities, capital expenditures, selling, general and administrative costs, facilities expansion, and to meet working capital needs. We expect from time to time to evaluate the acquisition of businesses, products and technologies for which a portion of the net proceeds may be used, although we currently are not planning or negotiating any such transactions.

The amounts actually expended for each purpose may vary significantly depending upon numerous factors, including the amount and timing of the proceeds from this offering and progress with the development of our products. Expenditures will also depend upon the establishment of collaborative arrangements with other companies, the availability of additional financing and other factors. Investors will be relying on the judgment of our management regarding the application of the proceeds of any sale of shares of our common stock.

As of the date of this prospectus supplement, we cannot specify with certainty all of the particular uses of the proceeds from this offering. Accordingly, we will retain broad discretion over the use of such proceeds. Pending the use of the net proceeds from this offering as described above, we intend to invest the net proceeds in investment-grade, interest-bearing securities.

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PRICE RANGE OF COMMON STOCK

Our common stock trades on The NASDAQ Capital Market under the symbol “CBIO.” The last reported sale price for our common stock on December 18, 2017 was $10.57 per share. As of December 18, 2017, we had approximately 61 holders of record of our common stock. The number of record holders was determined from the records of our transfer agent and does not include beneficial owners of common stock whose shares are held in the names of various security brokers, dealers, and registered clearing agencies. A description of the common stock that we are issuing in this offering is set forth under the heading “Description of Capital Stock” beginning on page 8 of the accompanying base prospectus.

The following table sets forth for the periods indicated the high and low sale prices per share of our common stock as reported on The Nasdaq Capital Market, but as adjusted to reflect applicable reverse stock splits:

The market price of our common stock has been and may continue to be subject to wide fluctuations in response to a number of events and factors, such as progress in our development programs, quarterly variations in our operating results, announcements of technological innovations or new products by us or our competitors, changes in financial estimates and recommendations by securities analysts, the operating and stock performance of other companies that investors may deem comparable to us, and news reports relating to trends in our markets. These fluctuations, as well as general economic and market conditions, may adversely affect the market price for our common stock.

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UNDERWRITING

Under the terms and subject to the conditions set forth in an underwriting agreement, the underwriters named below, for whom JonesTrading Institutional Services LLC is acting as representative, have agreed, severally and not jointly, to purchase, and we have agreed to sell to them, the number of shares of common stock indicated below:

The underwriting agreement provides that the obligations of the several underwriters are subject to various conditions, including the approval of certain legal matters by their counsel. The underwriters are obligated to take and pay for all the shares of common stock offered by this prospectus supplement if any such shares are purchased. However, the underwriters are not required to take or pay for the shares of common stock covered by the underwriters’ option to purchase additional securities described below.

The underwriters expect to deliver the shares of common stock to purchasers on or about December 22, 2017.

The public offering price was determined in negotiations between the underwriter and us based on the closing price per share of our common stock on the Nasdaq Capital Market on December 19, 2017, which was $9.96 per share. The following table shows the per share and total public offering price, underwriting discounts and commissions, and proceeds before expenses to us.

The estimated offering expenses payable by us, exclusive of the underwriting discounts and commissions, are approximately $145,000. We have agreed to pay the expenses of the underwriters in connection with the offering, including filing fees, investor presentation expenses and underwriters’ counsel legal fees, up to an aggregate maximum amount of $50,000.

The underwriters have informed us that they do not intend to confirm sales to any discretionary accounts over which they exercise discretionary authority.

The underwriters will require all our directors and officers to agree not to offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, any shares of common stock or any securities convertible into or exchangeable or exercisable for shares of common stock, or, collectively, the Lock-Up Securities, without the prior written consent of the representative for a period of 45 days from the date of this prospectus supplement. These restrictions are subject to certain exceptions, including if the transfer (i) does not trigger any filing or reporting requirement or obligation or result in any other voluntary or mandatory public disclosure, including but not limited to Form 4 of Section 16 of the Securities Exchange Act of 1934, as amended, (ii) is a gift, (iii) is by process of will or intestacy, (iv) is a distribution to partners, members or shareholders of the undersigned, (v) is to a settlor of a trust or to the estate of a beneficiary of a trust, (vi) relates to the transfer of shares of common stock to the Company pursuant to an agreement under which the Company has the option to repurchase shares or

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has a right of first refusal, (vii) is pursuant to a pre-existing trading plan, (viii) is in satisfaction of tax withholding obligations, (ix) is pursuant to a liquidation, tender offer, merger, consolidation, binding share exchange or other similar transaction involving a change in control of the Company, (x) is pursuant to a court order or settlement agreement related to the distribution of assets in connection with the dissolution of marriage or civil union, or (xi) relates to the exercise of any option, warrant or other right to acquire shares of common stock, the settlement of any stock-settled stock appreciation rights, restricted stock or restricted stock units, including through a “net” or cashless exercise, granted and outstanding as of the date of the lock-up agreement or at the closing date of the offering contemplated by this prospectus supplement, or the conversion of any convertible security of the Company in accordance with its terms; provided, however, that it shall be a condition to the transfer pursuant to clauses (i), (ii), (iii), (iv), (v), (ix) and (x) that the transferee execute an agreement stating that the transferee is receiving and holding the securities subject to the provisions of such lock-up agreement.

We have agreed, subject to certain exceptions, that from the date of this prospectus supplement to, but not including, January 31, 2018, we will not, without the prior written consent of the representative, directly or indirectly offer, pledge, sale, contract to sell, short sale or otherwise dispose of any shares of common stock or other securities convertible into or exchangeable or exercisable for shares of common stock or derivative of common stock. These restrictions do not apply among others to (i) the sale of shares of common stock to the underwriters; (ii) the issuance of shares of common stock upon exercise, conversion or exchange of options or upon the conversion or exchange of other securities; (iii) the filing of one or more registration statements registering the secondary sale of shares of common stock or securities convertible into shares of common stock; (iv) the sale of shares of common stock, options to purchase shares of common stock, restricted stock units or similar equity securities pursuant to any stock option, stock bonus or other stock plan or arrangement described in the accompanying prospectus; (v) the issuance of shares of common stock, options, restricted stock units or similar equity securities to our directors as compensation for their services as directors of the company; (vi) agreements providing for the issuance of shares of common stock or any securities convertible into or exchangeable or exercisable for shares of common stock in connection with the acquisition by the Company or any of its subsidiaries of the securities, business, property or other assets of another person or entity (including pursuant to an employee benefit plan assumed by the Company in connection with such acquisition), and the issuance of any such securities pursuant to any such agreement, and (vii) agreements providing for the issuance of shares of common stock or any security convertible into or exercisable for shares of common stock in connection with joint ventures, commercial relationships, debt financing or other strategic transactions, and issuance of any such securities pursuant to any such agreements; provided that in the case of clauses (vi) and (vii), the aggregate number of shares of common stock that the Company may sell or issue or agree to sell or issue pursuant to clauses (vi) and (vii), taken together, shall not exceed 5.0% of the total number of shares of common stock issued and outstanding immediately subsequent to the completion of the transactions contemplated by this prospectus supplement.

The representative of the underwriters has advised us that they propose to offer the shares of common stock to the public at the offering price set forth on the cover page of this prospectus supplement and to certain dealers at that price less a concession not in excess of $0.38 per share of common stock. After the offering, the offering price, concession and reallowance to dealers may be reduced by the representative. In order to facilitate the offering of the shares of common stock, the underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the shares of common stock. Specifically, the underwriters may sell more shares than they are obligated to purchase under the underwriting agreement, creating a short position. A short sale is covered if the short position is no greater than the number of shares available for purchase by the underwriters under the option to purchase additional securities. The underwriters can close out a covered short sale by exercising the option to purchase additional securities or purchasing shares in the open market. In determining the source of shares to close out a covered short sale, the underwriters will consider, among other things, the open market price of shares compared to the price available under the option to purchase additional securities. The underwriters may also sell shares in excess of the option to purchase additional securities, creating a naked short position. The underwriters must close out any naked short position by purchasing shares in the open market.

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A naked short position is more likely to be created if the underwriters are concerned that there may be downward pressure on the price of the shares of common stock in the open market after pricing that could adversely affect investors who purchase in this offering. As an additional means of facilitating this offering, the underwriters may bid for, and purchase, shares of common stock in the open market to stabilize the price of the shares of common stock. These activities may raise or maintain the market price of the shares of common stock above independent market levels or prevent or retard a decline in the market price of the shares of common stock. The underwriters are not required to engage in these activities and may end any of these activities at any time.

We have agreed to indemnify the underwriters against certain liabilities, including liabilities under the Securities Act.

The underwriters and their respective affiliates are full-service financial institutions engaged in various activities, which may include securities trading, commercial and investment banking, financial advisory, investment management, investment research, principal investment, hedging, financing and brokerage activities. The underwriters and certain of their affiliates have provided from time to time, and may provide in the future, investment and commercial banking and financial advisory services to us and our affiliates in the ordinary course of business, for which they have received and may continue to receive customary fees and commissions. In the ordinary course of their various business activities, the underwriters and their respective affiliates may make or hold a broad array of investments and actively trade debt and equity securities (or related derivative securities) and financial instruments (including bank loans) for their own account and for the accounts of their customers, and such investment and securities activities may involve securities and/or instruments of ours. The underwriters and their respective affiliates may also make investment recommendations and/or publish or express independent research views in respect of such securities or instruments and may at any time hold, or recommend to clients that they acquire, long and/or short positions in such securities and instruments.

In connection with this offering, we granted JonesTrading Institutional Services LLC a right of first refusal to act as joint lead managing underwriter or joint book runner for a qualifying equity offering, for the earlier of (a) a period of six months following the completion of the offering or (b) the occurrence of a qualifying equity offering. The terms of any such engagement will be determined by separate agreement.

Selling Restrictions

Notice to Prospective Investors in Canada

Shares of our common stock may be sold only to purchasers purchasing, or deemed to be purchasing, as principal that are accredited investors, as defined in National Instrument 45-106 Prospectus Exemptions or subsection 73.3(1) of the Securities Act (Ontario), and are permitted clients, as defined in National Instrument 31-103 Registration Requirements, Exemptions and Ongoing Registrant Obligations. Any resale of the shares of our common stock must be made in accordance with an exemption from, or in a transaction not subject to, the prospectus requirements of applicable securities laws.

Securities legislation in certain provinces or territories of Canada may provide a purchaser with remedies for rescission or damages if this prospectus supplement and the accompanying base prospectus (including any amendment thereto) contains a misrepresentation, provided that the remedies for rescission or damages are exercised by the purchaser within the time limit prescribed by the securities legislation of the purchaser’s province or territory. The purchaser should refer to any applicable provisions of the securities legislation of the purchaser’s province or territory for particulars of these rights or consult with a legal advisor.

Pursuant to section 3A.3 (or, in the case of securities issued or guaranteed by the government of a non-Canadian jurisdiction, section 3A.4) of National Instrument 33-105 Underwriting Conflicts (NI 33-105), the underwriters are not required to comply with the disclosure requirements of NI 33-105 regarding underwriter conflicts of interest in connection with this offering.

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LEGAL MATTERS

The validity of the securities being offered by this prospectus will be passed upon by Morrison & Foerster LLP, Palo Alto, California. The underwriters being represented in connection with this offering by Duane Morris LLP, Newark, New Jersey.

EXPERTS

The consolidated balance sheets of Catalyst Biosciences, Inc. as of December 31, 2016 and 2015, and the related consolidated statements of operations, comprehensive loss, convertible preferred stock and stockholders’ equity (deficit), and cash flows for each of the years then ended, have been audited by EisnerAmper LLP, independent registered public accounting firm, as stated in their report which is incorporated by reference herein. Such financial statements have been incorporated by reference herein in reliance on the report of such firm given upon their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

This prospectus supplement and the accompanying base prospectus are part of a registration statement on Form S-3 that we filed with the SEC under the Securities Act. This prospectus supplement and the accompanying base prospectus do not contain all of the information included in the registration statement. We have omitted certain parts of the registration statement in accordance with the rules and regulations of the SEC. For further information, we refer you to the registration statement, including its exhibits and schedules. Statements contained in this prospectus supplement and the accompanying base prospectus about the provisions or contents of any contract, agreement or any other document referred to are not necessarily complete. Please refer to the actual exhibit for a more complete description of the matters involved.

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings, including the registration statement and exhibits, are available to the public at the SEC’s website at http://www.sec.gov. You may also read, without charge, and copy the documents we file, at the SEC’s public reference rooms at 100 F Street, N.E., Room 1580, Washington, D.C. 20549. You can request copies of these documents by writing to the SEC and paying a fee for the copying cost. Please call the SEC at 1-800-SEC-0330 for further information on the public reference rooms.

We maintain an Internet site at www.catalystbiosciences.com. Webcasts of presentations we make at certain conferences may also be available on our website from time to time. We have not incorporated by reference into this prospectus supplement or the accompanying base prospectus the information on our website, and you should not consider any of the information posted on or hyper-linked to our website to be a part of this prospectus supplement or the accompanying base prospectus.

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INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

The SEC allows us to “incorporate by reference” the information we file with the SEC, which means we can disclose important information to you by referring you to those documents. The information we incorporate by reference is an important part of this prospectus, and certain information that we will later file with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below as well as any future filings made with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act after the date of this prospectus until we sell all of the securities under this prospectus, except that we do not incorporate any document or portion of a document that is “furnished” to the SEC, but not deemed “filed.” The following documents filed with the SEC are incorporated by reference in this prospectus:

We also incorporate by reference into this prospectus supplement additional documents that we may file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, excluding, in each case, information deemed furnished and not filed until we sell all of the securities we are offering. Any statements contained in a previously filed document incorporated by reference into this prospectus supplement or the accompanying base prospectus is deemed to be modified or superseded for purposes of this prospectus supplement and the accompanying base prospectus to the extent that a statement contained in this prospectus supplement, or in a subsequently filed document also incorporated by reference herein, modifies or supersedes that statement.

We will provide to you at no cost a copy of any and all of the information incorporated by reference into the registration statement of which this prospectus supplement is a part. You may make a request for copies of this information in writing or by telephone. Requests should be directed to:

Catalyst Biosciences, Inc.

260 Littlefield Ave.

South San Francisco, CA 94080

Attn: Fletcher Payne, Chief Financial Officer

(650) 871-0761

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$50,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Units

INVESTING IN OUR SECURITIES INVOLVES A HIGH DEGREE OF RISK. YOU SHOULD CAREFULLY READ AND CONSIDER THE RISK FACTORS DESCRIBED IN THIS PROSPECTUS, ANY ACCOMPANYING PROSPECTUS SUPPLEMENT AND IN THE DOCUMENTS INCORPORATED BY REFERENCE INTO THIS PROSPECTUS. SEE “RISK FACTORS” BEGINNING ON PAGE 3.

From time to time, we may offer and sell, in one or more offerings, in amounts, at prices and on terms determined at the time of any such offering, common stock, preferred stock, debt securities, warrants, either individually or in units, with a total value of up to $50,000,000.

Our common stock trades on the NASDAQ Capital Market under the symbol “CBIO.” On March 1, 2016, the last reported sale price of the common stock on the NASDAQ Capital Market was $2.15 per share.

As of January 26, 2016, the aggregate market value of our outstanding common stock held by non-affiliates, or the public float, was approximately $20.8 million based on 11,430,104 shares of outstanding stock, of which 9,035,828 are held by non-affiliates, and a per share price of $2.30, which was the closing sale price of our common stock on January 26, 2016. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sell our common stock in a public primary offering with a value exceeding more than one-third of our public float in any 12-month period so long as our public float remains below $75,000,000. We have not offered any securities pursuant to General Instruction I.B.6 of Form S-3 during the prior 12 calendar month period that ends on and includes the date of this prospectus. As of January 26, 2016, one-third of our public float is equal to approximately $6.9 million.

We will provide specific terms of these securities in supplements to this prospectus. The prospectus supplement will also describe the specific manner in which we will offer the securities and may also supplement, update or amend information contained in this document. You should read this prospectus and any supplement carefully before you purchase any of our securities.

THIS PROSPECTUS MAY NOT BE USED TO OFFER AND SELL SECURITIES UNLESS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

We may offer the securities in amounts, at prices and on terms determined at the time of offering. We may sell the securities directly to you, through agents we select or through underwriters and dealers we select. If we use agents, underwriters or dealers to sell the securities, we will name them and describe their compensation in a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is April 28, 2016

TABLE OF CONTENTS

No person has been authorized to give any information or make any representations in connection with this offering other than those contained or incorporated by reference in this prospectus and any accompanying prospectus supplement in connection with the offering described in this prospectus and any accompanying prospectus supplement, and, if given or made, such information or representations must not be relied upon as having been authorized by us. Neither this prospectus nor any prospectus supplement shall constitute an offer to sell or a solicitation of an offer to buy offered securities in any jurisdiction in which it is unlawful for such person to make such an offering or solicitation. Neither the delivery of this prospectus or any prospectus supplement nor any sale made hereunder shall under any circumstances imply that the information contained or incorporated by reference in this prospectus or in any prospectus supplement is correct as of any date subsequent to the date of this prospectus supplement or of any prospectus supplement.

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we filed with the Securities and Exchange Commission, or SEC, using a “shelf” registration process. Under this shelf registration process, we may, from time to time, issue and sell to the public any part of the securities described in this prospectus in one or more offerings up to a total dollar amount of $50,000,000.

This prospectus provides you with a general description of the securities we may offer. Each time we sell the securities, we will provide a prospectus supplement containing specific information about the terms of that offering. The prospectus supplement may also add, update or change information in this prospectus or in documents incorporated by reference in this prospectus. To the extent that any statement that we make in a prospectus supplement is inconsistent with statements made in this prospectus or in documents incorporated by reference in this prospectus, the statements made or incorporated by reference in this prospectus will be deemed modified or superseded by those made in the prospectus supplement. You should carefully read both this prospectus and any prospectus supplement together with the additional information described under the heading “Where You Can Find More Information” before buying any securities offered in this offering.

THIS PROSPECTUS MAY NOT BE USED TO OFFER AND SELL SECURITIES UNLESS IT IS ACCOMPANIED BY A PROSPECTUS SUPPLEMENT.

For purposes of this prospectus, references to the terms “Catalyst,” “the Company,” “we,” “us” and “our” refer to Catalyst Biosciences, Inc., unless the context otherwise requires.

The registration statement containing this prospectus, including exhibits to the registration statement, provides additional information about us and the securities offered under this prospectus. The registration statement can be read at the SEC’s website or at the SEC offices mentioned under the heading “Where You Can Find More Information.”

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ABOUT CATALYST

We are a clinical-stage biopharmaceutical company focused on creating and developing novel medicines to address serious medical conditions. To date, we have focused our product development efforts in the fields of hemostasis, including the treatment of hemophilia and surgical bleeding, and inflammation, including prevention of delayed graft function in renal transplants and the treatment of dry age-related macular degeneration, a condition that can cause visual impairment or blindness for which there are no approved treatments. Our most advanced program is an improved next-generation coagulation Factor VIIa variant, CB 813d, that has successfully completed a Phase 1 clinical trial in severe hemophilia A and B patients. In addition to our lead Factor VIIa program, we have two other next-generation coagulation factors, a Factor IX variant, CB 2679d/ISU 304, that is in advanced preclinical development, and a Factor Xa variant, that has reached the advanced lead preclinical stage of development. Proteases regulate several complex biological cascades, or sequenced biochemical reactions, including the coagulation cascade that controls bleeding (hemostasis) in hemophilia and non-hemophilia settings and the complement cascade that causes inflammation and tissue damage in certain diseases.

Additional details of these programs and related strategic agreements are contained in our Annual Report on Form 10-K for the year ended December 31, 2015.

We commenced operations in 2002 and are a Delaware corporation. On August 20, 2015, we completed our business combination with Targacept, Inc., which was incorporated in 1997. Following the completion of the merger, our business conducted became primarily the business conducted by Old Catalyst. We refer in this prospectus to the business combination as the “merger” to the Company prior to the merger as “Targacept” and to our subsidiary as “Old Catalyst,” and discussions of historical results reflect the results of Old Catalyst prior to the completion of the merger and do not include the historical results of Targacept prior to the completion of the Merger.

Our corporate headquarters are located at South San Francisco, California 94080. Our telephone number is (650) 266-8674, and our website address is www.catalystbiosciences.com. The information on or accessible through our website does not constitute part of this prospectus or any accompanying prospectus supplement and should not be relied upon in connection with making any investment in our securities. We make our annual reports on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and amendments to these reports available free of charge on our website as soon as reasonably practicable after we file these reports with the Commission. Our Code of Ethics can be found on our website.

Securities We Are Offering

We may offer shares of common stock, shares of preferred stock, debt securities, warrants, either individually or in units, with a total value of up to $50,000,000 from time to time under this prospectus at prices and on terms to be determined by market conditions at the time of the offering. Our common stock currently is quoted on the NASDAQ Capital Market under the symbol “CBIO.” Shares of common stock that may be offered in this offering will, when issued and paid for, be fully paid and non-assessable.

We refer to our common stock, preferred stock, debt securities, warrants and units in this prospectus as “securities.” This prospectus provides you with a general description of the securities we may offer. Each time we offer a type or series of securities, we will provide a prospectus supplement that will describe the specific amounts, prices and other important terms of the securities, as described below under “Plan of Distribution.”

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Any such forward-looking statements are not guarantees of future performance and actual results, developments and business decisions may differ from those contemplated by such forward-looking statements. We disclaim any duty to update any forward-looking statements. You should also carefully consider other information set forth in reports or other documents that we file with the Commission.

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specify in the applicable prospectus supplement, holders of the warrants may exercise the warrants at any time up to 5:00 P.M. Eastern Time on the expiration date that we set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

Holders of the warrants may exercise the warrants by delivering the warrant certificate representing the warrants to be exercised together with specified information, and paying the required amount to the warrant agent in immediately available funds, as provided in the applicable prospectus supplement. We will set forth on the reverse side of the warrant certificate and in the applicable prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent.

Upon receipt of the required payment and the warrant certificate properly completed and duly executed at the corporate trust office of the warrant agent or any other office indicated in the applicable prospectus supplement, we will issue and deliver the securities purchasable upon such exercise. If fewer than all of the warrants represented by the warrant certificate are exercised, then we will issue a new warrant certificate for the remaining amount of warrants. If we so indicate in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Enforceability of Rights by Holders of Warrants

Any warrant agent will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

Outstanding Warrants

Old Catalyst previously issued (i) warrants to purchase shares of Series A convertible preferred stock in 2005 in connection with a loan, (ii) warrants to purchase shares of Series E convertible preferred stock in 2014 in connection with the issuance of Series E convertible preferred stock, and (iii) warrants to purchase shares of Series F convertible preferred stock in 2015 in connection with the issuance of convertible promissory notes. In connection with the merger, such warrants were assumed by us and are now exercisable, respectively, (i) at any time until the 7-year anniversary of the merger for an aggregate of 1,289 shares of our common stock at an exercise price of $26.18 per share, (ii) at any time until the 5-year anniversary of the original date of issuance for an aggregate of 37,554 shares of our common stock at an exercise price of $33.27 per share, and (iii) at any time until the 5-year anniversary of the original date of issuance for an aggregate of 142,111 shares of our common stock at an exercise price of for $3.33 per share.

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We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only in the form of a global security, an investor should be aware of the following:

There may be more than one financial intermediary in the chain of ownership for an investor. We do not monitor and are not responsible for the actions of any of those intermediaries.

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks or brokers to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

The global security will terminate when the following special situations occur:

The prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

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PLAN OF DISTRIBUTION

We may sell the securities being offered by this prospectus separately or together through any of the following methods:

We may distribute securities from time to time in one or more transactions:

We will describe the method of distribution of the securities in the applicable prospectus supplement. We may also determine the price or other terms of the securities offered under this prospectus by use of an electronic auction. We will describe how any auction will determine the price or any other terms, how potential investors may participate in the auction and the nature of the obligations of the underwriter, dealer or agent in the applicable prospectus supplement.

Unless otherwise specified in the applicable prospectus supplement, each class or series of securities will be a new issue with no established trading market, other than our common stock, which is traded on the NASDAQ Capital Market. We may elect to list any other class or series of securities on any exchange, but we are not obligated to do so. It is possible that one or more underwriters may make a market in a class or series of securities, but the underwriters will not be obligated to do so and may discontinue any market making at any time without notice. We cannot give any assurance as to the liquidity of the trading market for any of the securities.

Underwriters, dealers or agents may receive compensation in the form of discounts, concessions or commissions from us or our purchasers (as their agents in connection with the sale of the securities). In addition, underwriters may sell the securities to or through dealers, and those dealers may receive compensation in the form of discounts, concessions or commissions from the underwriters and/or commissions from the purchasers for whom they act as agent. These underwriters, dealers or agents may be considered to be underwriters under the Securities Act. As a result, discounts, commissions, or profits on resale received by the underwriters, dealers or agents may be treated as underwriting discounts and commissions. The prospectus supplement will identify any such underwriter, dealer or agent, and describe any compensation received by them from us. Only underwriters named in the prospectus supplement are underwriters of the securities offered by the prospectus supplement. Any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers may be changed from time to time.

We may sell the securities directly or through agents we designate from time to time. We will name any agent involved in the offering and sale of securities and we will describe any commissions we will pay the agent in the prospectus supplement. Unless the prospectus supplement states otherwise, our agent will act on a best-efforts basis for the period of its appointment.

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LEGAL MATTERS

The validity of the securities being offered by this prospectus will be passed upon by Morrison & Foerster LLP of Palo Alto, CA. Additional legal matters may be passed upon for us or any underwriters, dealers or agents, by counsel that we will name in an applicable prospectus supplement.

EXPERTS

The consolidated balance sheets of Catalyst Biosciences, Inc. as of December 31, 2015 and 2014, and the related consolidated statements of operations, comprehensive loss, convertible preferred stock and stockholders’ equity (deficit) and cash flows for each of the years in the three-year period ended December 31, 2015, have been audited by EisnerAmper LLP, independent registered public accounting firm, as stated in their report which is incorporated herein by reference. Such financial statements have been incorporated herein by reference in reliance on the report of such firm given upon their authority as experts in accounting and auditing.

WHERE YOU CAN FIND MORE INFORMATION

We are a reporting company and file annual, quarterly and current reports, proxy statements and other information with the Securities and Exchange Commission, or the SEC. You may read and copy these reports, proxy statements and other information at the SEC’s public reference rooms at 100 F Street, N.E., Room 1580, Washington, D.C. 20549. You can request copies of these documents by writing to the SEC and paying a fee for the copying cost. Please call the SEC at 1-800-SEC-0330 for more information about the operation of the public reference rooms. Our SEC filings are also available at the SEC’s website at www.sec.gov and our website at www.catalystbiosciences.com. We have not incorporated by reference into this prospectus the information contained on our website and you should not consider it to be part of this prospectus. In addition, you can read and copy our SEC filings at the office of the National Association of Securities Dealers, Inc. at 1735 K Street, Washington, D.C. 20006.

We have filed a registration statement on Form S-3 with the SEC relating to the securities covered by this prospectus. This prospectus is a part of the registration statement and does not contain all of the information in the registration statement. You may review a copy of the registration statement at the SEC’s public reference room in Washington, D.C., as well as through the SEC’s Internet site at www.sec.gov.

The SEC allows us to “incorporate by reference” the information we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this prospectus. In addition, information we file with the SEC in the future will automatically update and supersede information contained in this prospectus and any accompanying prospectus supplement.

This prospectus incorporates by reference the documents set forth below that we have previously filed with the SEC:

We also incorporate by reference into this prospectus additional documents that we may file with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, excluding, in each case, information deemed furnished and not filed until we sell all of the securities we are offering. Any statements contained in a previously filed document incorporated by reference into this prospectus is deemed to be modified or superseded for purposes of this prospectus to the extent that a statement contained in this prospectus, or in a subsequently filed document also incorporated by reference herein, modifies or supersedes that statement.

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We will provide to you at no cost a copy of any and all of the information incorporated by reference into the registration statement of which this prospectus is a part. You may make a request for copies of this information in writing or by telephone. Requests should be directed to:

Catalyst Biosciences, Inc.

260 Littlefield Ave.

South San Francisco, CA 94080

Attn: Fletcher Payne, Chief Financial Officer

(650) 871-0761

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1,105,263 Shares

Common Stock

PROSPECTUS SUPPLEMENT

JonesTrading

Ladenburg Thalmann

LifeSci Capital

December 20, 2017