ASSEMBLY BIOSCIENCES INC

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934 (Amendment No. )

Assembly Biosciences, Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

Two Tower Place, 7th Floor

South San Francisco, California 94080

NOTICE OF 2024 ANNUAL MEETING OF STOCKHOLDERS

To Be Held Wednesday, May 29, 2024

April 17, 2024

Dear Stockholders:

You are cordially invited to attend the 2024 Annual Meeting of Stockholders (the Annual Meeting) of Assembly Biosciences, Inc., a Delaware corporation (we, us, Assembly or the Company). The Annual Meeting will be held on Wednesday, May 29, 2024 at 8:00 a.m. Pacific Daylight Time (PDT) solely by remote communication (i.e., a virtual-only stockholder meeting) atwww.virtualshareholdermeeting.com/ASMB2024. During the meeting, stockholders will be asked to:

Elect the ten nominees named in the attached proxy statement to our Board of Directors (the Board);

Approve, on a non-binding advisory basis, our named executive officers’ compensation, as disclosed in the proxy statement accompanying this notice;

Vote, on a non-binding advisory basis, on the frequency of future advisory votes to approve our named executive officers’ compensation;

Ratify the selection of Ernst & Young LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2024;

Approve the Assembly Biosciences, Inc. Amended and Restated 2018 Stock Incentive Plan to increase the number of shares reserved for issuance thereunder by 220,000 shares;

Approve the Assembly Biosciences, Inc. Second Amended and Restated 2018 Employee Stock Purchase Plan to increase the number of shares reserved for issuance thereunder to 164,500 shares and remove the maximum number of shares purchasable under the plan per offering period;

Vote on such other matters that may properly come before the meeting and any adjournment or postponement thereof.

These matters are more fully described in the proxy statement accompanying this notice.

Our Board has fixed the close of business on April 1, 2024 as the record date for the determination of stockholders entitled to notice of and to vote at the Annual Meeting and any adjournment or postponement thereof. See the attached proxy statement for information on how to attend the virtual Annual Meeting and vote during the meeting.

To ensure your representation at the Annual Meeting, you are requested to submit your vote as instructed in the Notice of Internet Availability of Proxy Materials that will be sent to you. You may also request a paper proxy card at any time on or before May 15, 2024 to submit your vote by mail. If you attend and vote at the Annual Meeting your proxy will not be used.

We hope that you will attend the virtual Annual Meeting, and we very much appreciate your continuing interest in our Company.

By Order of the Board of Directors,

Jason A. Okazaki

Chief Executive Officer and President

Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting to be held solely by remote communication atwww.virtualshareholdermeeting.com/ASMB2024 on Wednesday, May 29, 2024

at 8:00 a.m. PDT.

The proxy statement and the Annual Report for the fiscal year ended December 31, 2023

are available at: www.proxyvote.com.

You are cordially invited to attend the Annual Meeting by remote communication. Whether or not you expect to attend the Annual Meeting, please vote over the Internet using your 16-digit control number as instructed in your Notice of Internet Availability of Proxy Materials or proxy card or vote by mail by requesting a printed copy of the proxy card. Even if you have voted by proxy, you may still vote at the Annual Meeting if you attend by remote communication. Please note, however, that if you hold your shares through a broker or nominee and you wish to vote at the Annual Meeting, you must obtain your control number from your broker or nominee to vote.

Two Tower Place, 7th Floor

South San Francisco, California 94080

PROXY STATEMENT

FOR THE 2024 ANNUAL MEETING OF STOCKHOLDERS

May 29, 2024

INFORMATION CONCERNING SOLICITATION AND VOTING

The Board of Directors (the Board) of Assembly Biosciences, Inc., a Delaware corporation (we, us, Assembly Bio, Assembly or the Company), is soliciting your proxy to vote at the 2024 Annual Meeting of Stockholders (the Annual Meeting) to be held on Wednesday, May 29, 2024 at 8:00 a.m. Pacific Daylight Time (PDT) solely by remote communication (i.e., a virtual-only stockholder meeting) atwww.virtualshareholdermeeting.com/ASMB2024. Any adjournments or postponements of the meeting will also be held by remote communication at the same location.

You are invited to attend the Annual Meeting to vote on the proposals described in this proxy statement. However, you do not need to attend the meeting to vote your shares. Instead, you may follow the instructions in the Notice of Internet Availability of Proxy Materials (the Proxy Availability Notice) described below to submit your proxy through the Internet, or you may vote by mail by using the proxy card provided or requesting a printed copy of the proxy card.

We sent the Proxy Availability Notice on or about April 17, 2024 to our stockholders of record and beneficial owners as of April 1, 2024, the record date for the Annual Meeting. The proxy materials, including this proxy statement, proxy card or voting instruction card and our Annual Report for the fiscal year ended December 31, 2023 are being distributed and made available on or about April 17, 2024. This proxy statement contains important information for you to consider when deciding how to vote on the matters brought before the Annual Meeting. Please read it carefully.

This proxy statement and the Proxy Availability Notice contain instructions for accessing and reviewing our proxy materials on the Internet and for voting by proxy over the Internet, by phone or by mail. The Proxy Availability Notice and the proxy card also will provide instructions on how you can elect to receive future proxy materials electronically or in printed form by mail. If you choose to receive future proxy materials electronically, you will receive an email next year with instructions containing a link to the proxy materials and a link to the proxy voting site. Your election to receive proxy materials electronically or in printed form by mail will remain in effect until you terminate such election. You will need to obtain your own Internet access if you choose to access the proxy materials and/or vote over the Internet. If you prefer to receive printed copies of our proxy materials, the Proxy Availability Notice contains instructions on how to request the materials by mail. For stockholders who have elected to receive proxy materials electronically, you will not receive printed copies of the proxy materials unless you request them. If you elect to receive the materials by mail, you may also vote by proxy on the proxy card or voter instruction card that you will receive in response to your request.

Choosing to receive future proxy materials electronically will allow us to provide you with the information you need more rapidly, will save us the cost of printing and mailing documents to you and will conserve natural resources.

TABLE OF CONTENTS

i

ii