DEF 14A

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

Filed by the Registrant☒

Filed by a Party other than the Registrant☐

Check the appropriate box:


☐	Preliminary Proxy Statement


☐	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))


☒	Definitive Proxy Statement


☐	Definitive Additional Materials


☐	Soliciting Material Under §240.14a-12

SYNLOGIC, INC.

(Name of Registrant as Specified In Its Charter)

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

Payment of Filing Fee (Check the appropriate box):


☒	No fee required.


☐	Fee paid previously with preliminary materials.


☐	Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11.

November 12, 2025

To Our Stockholders:

You are cordially invited to attend the 2025 Annual Meeting of Stockholders (“Annual Meeting”) of Synlogic, Inc. (“Synlogic”). The meeting will be held on December 15, 2025 at 9:00 a.m. ET. The Annual Meeting will be held in a virtual meeting format only. You can attend the Annual Meeting online, vote your shares electronically, and submit your questions during the Annual Meeting by visiting www.virtualshareholdermeeting.com/SYBX2025 and entering your 16-digit control number found on the Notice of Internet Availability or the proxy card that you receive. For further information about the Annual Meeting, please see the Information About the Annual Meeting and Voting beginning on page 3. You will not be able to attend the Annual Meeting in person.

The agenda for this Annual Meeting includes (i) the election of two (2) Class I directors, to serve a three-year term, (ii) an advisory vote on the compensation paid to our named executive officer (iii) the approval of the Synlogic, Inc. 2025 Equity Incentive Plan and (iv) the ratification of the appointment of KPMG LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2025. Our Board of Directors recommends the election of the nominees to our Board of Directors and a vote in favor of proposals (ii), (iii) and (iv). Such other business will be transacted as may properly come before the Annual Meeting.

We hope you will be able to attend the Annual Meeting. Whether you plan to attend the Annual Meeting or not, it is important that you cast your vote. You may vote over the Internet as well as by telephone or by mail. When you have finished reading the proxy statement, you are urged to vote in accordance with the instructions set forth in this proxy statement. We encourage you to vote by proxy so that your shares will be represented and voted at the meeting.

Thank you for your continued support of Synlogic, Inc. We look forward to you joining us at this year’s Annual Meeting.

Sincerely,

Mary Beth Dooley

Principal Executive Officer & Principal Financial Officer

November 12, 2025

NOTICE OF 2025 ANNUAL MEETING OF STOCKHOLDERS



Time:		9:00 a.m. Eastern Time
Date:		December 15, 2025
Virtual Meeting:		The Annual Meeting will be a virtual meeting through which you can listen to the meeting, submit questions and vote online. You may access the Annual Meeting by visiting www.virtualshareholdermeeting.com/SYBX2025 and entering the control number (included in the proxy card that you receive). Stockholders attending the virtual meeting will be afforded the same rights and opportunities to participate as they would at an in-person meeting.

Purpose:		(1) To elect two Class I directors to serve a three-year term expiring in 2028; (2) To approve by an advisory vote the compensation of the Company’s named executive officers; (3) To approve the Synlogic, Inc. 2025 Equity Incentive Plan; (4) To ratify the appointment of KPMG LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2025; and (5) To transact such other business that is properly presented at the Annual Meeting and any adjournments or postponements thereof.

Who may vote:		You may vote if you were the record owner of Synlogic, Inc. common stock at the close of business on October 24, 2025 (the “Record Date”). A list of registered stockholders as of the close of business on the Record Date will be available at our corporate headquarters for examination by any stockholder for any purpose germane to the Annual Meeting for a period of at least 10 days prior to the Annual Meeting. If you wish to view this list, please contact me, as Corporate Secretary, at Synlogic, Inc., PO Box 30, Winchester, MA 01890. Such list will also be available for examination by the stockholders during the Annual Meeting at www.virtualshareholdermeeting.com/SYBX2025.

All stockholders are cordially invited to attend the virtual annual meeting. Whether you plan to attend the Annual Meeting or not, we urge you to vote and submit your proxy by the Internet, telephone or mail in order to ensure the presence of a quorum. You may change or revoke your proxy at any time before it is voted at the meeting.

By order of the Board of Directors,

Mary Beth Dooley

Principal Executive Officer & Principal Financial Officer

TABLE OF CONTENTS


		PAGE
Important Information About the Annual Meeting and Voting		2
Security Ownership of Certain Beneficial Owners and Management		7
Management and Corporate Governance		9
Executive Officer and Director Compensation		15
Pay Versus Performance		22
Equity Compensation Plan Information		25
Report of Audit Committee		27
Certain Relationships and Related Person Transactions		28
Election of Directors		29
Advisory Vote on Approval of Executive Compensation as Disclosed in This Proxy Statement		30
Approval of the Synlogic, Inc. 2025 Equity Incentive Plan		31
Independent Registered Public Accounting Firm		36
Code of Conduct and Ethics		38
Other Matters		39
Stockholder Proposals and Nominations For Director		40
Appendix A - Synlogic, Inc. 2025 Equity Incentive Plan		41

SYNLOGIC, INC.

PO Box 30

Winchester, MA 01890

PROXY STATEMENT FOR THE 2025 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON DECEMBER 15, 2025

This proxy statement, along with the accompanying notice of 2025 Annual Meeting of stockholders, contains information about the 2025 Annual Meeting of stockholders of Synlogic, Inc., including any adjournments or postponements of the Annual Meeting. We are holding the annual meeting at 9:00 a.m., Eastern Time, on December 15, 2025. You will be able to attend the annual meeting, vote and submit your questions during the meeting by visiting www.virtualshareholdermeeting.com/SYBX2025.

In this proxy statement, we refer to Synlogic, Inc. as “Synlogic,” “the Company,” “we”, and “us.”

This proxy statement relates to the solicitation of proxies by our Board of Directors, or Board, for use at the annual meeting.

On or about November 12, 2025, we intend to begin sending to our stockholders the attached notice of 2025 annual meeting of stockholders, the proxy statement, the enclosed proxy card and our 2024 Annual Report.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE STOCKHOLDER MEETING TO BE HELD ON DECEMBER 15, 2025

This proxy statement, the Notice of Annual Meeting of Stockholders, our form of proxy card and our 2024 Annual Report to stockholders are available for viewing, printing and downloading at www.proxyvote.com. To view these materials please have your 16-digit control number(s) available that appears on your proxy card. On this website, you can also elect to receive future distributions of our proxy statements and annual reports to stockholders by electronic delivery.

Additionally, you can find a copy of our Annual Report on Form 10-K, which includes our financial statements, for the fiscal year ended December 31, 2024 on the website of the Securities and Exchange Commission, or the SEC, at www.sec.gov, or in the “Financials” section of the “Investors & Media” section of our website at www.synlogictx.com. You may also obtain a printed copy of our Annual Report on Form 10-K, including our financial statements, free of charge, from us by sending a written request to: Attn: Investor Relations, Synlogic, Inc., PO Box 30, Winchester, MA 01890. Exhibits will be provided upon written request and payment of an appropriate processing fee.

IMPORTANT INFORMATION ABOUT THE ANNUAL MEETING AND VOTING

Why is the Company Soliciting My Proxy?

The Board of Synlogic is soliciting your proxy to vote at the 2025 Annual Meeting of stockholders to be held virtually via live webcast, on December 15, 2025, at 9:00 a.m. Eastern Time and any adjournments of the meeting, which we refer to as the Annual Meeting. The proxy statement along with the accompanying Notice of Annual Meeting of Stockholders summarizes the purposes of the meeting and the information you need to know to vote at the Annual Meeting. You will be able to participate in the annual meeting, vote your shares electronically and submit your questions during the live webcast of the meeting by visiting www.virtualshareholdermeeting.com/SYBX2025 and entering your 16-digit control number found on the enclosed voting form.

We have made available to you on the Internet or have sent you this proxy statement, the Notice of Annual Meeting of Stockholders, the proxy card and a copy of our Annual Report on Form 10-K for the fiscal year ended December 31, 2024 because you owned shares of Synlogic, Inc. common stock on the Record Date. The Company intends to commence distribution of the proxy materials to stockholders on or about November 12, 2025.

Why are you holding a Virtual Annual Meeting?

We believe that hosting a virtual meeting is in the best interest of our stockholders and enables increased stockholder attendance and participation. Stockholders attending the virtual meeting will be afforded the same rights and opportunities to participate as they would at an in-person meeting, including the ability to submit questions and comments and to vote.

What happens if there are technical difficulties during the Annual Meeting?

We will have technicians ready to assist you with any technical difficulties you may have accessing the virtual Annual Meeting, voting at the annual meeting or submitting questions at the annual meeting. If you encounter any difficulties accessing the virtual Annual Meeting during the check-in or meeting time, please call the technical support number that will be posted on the Virtual Stockholder Meeting log in page.

Who Can Vote?

Only stockholders of record at the close of business on October 24, 2025 are entitled to vote at the annual meeting. On this Record Date, there were 11,698,919 shares of our common stock outstanding and entitled to vote. Our common stock is our only class of voting stock.

If on October 24, 2025 your shares of our common stock were registered directly in your name with our transfer agent, Equiniti Trust Company, LLC, then you are a stockholder of record.

If on October 24, 2025 your shares were held, not in your name, but rather in an account at a brokerage firm, bank, dealer or other similar organization, then you are the beneficial owner of shares held in “street name” and the Notice is being forwarded to you by that organization. The organization holding your account is considered to be the stockholder of record for purposes of voting at the Annual Meeting. As a beneficial owner, you have the right to direct your broker or other agent regarding how to vote the shares in your account. You are also invited to attend the annual meeting. However, since you are not the stockholder of record, you may not vote your shares at the annual meeting unless you request and obtain a valid proxy from your broker or other agent.

You do not need to attend the annual virtual meeting to vote your shares. Shares represented by valid proxies, received in time for the virtual annual meeting and not revoked prior to the annual meeting, will be voted at the annual meeting. For instructions on how to change or revoke your proxy, see “May I Change or Revoke My Proxy?” below.

How Many Votes Do I Have?

Each share of our common stock that you own entitles you to one vote.

How Do I Vote?

Whether you plan to attend the annual meeting or not, we urge you to vote by proxy. All shares represented by valid proxies that we receive through this solicitation, and that are not revoked, will be voted in accordance with your instructions on the proxy card or as instructed via Internet or telephone. You may specify whether your shares should be voted for or withheld for

each nominee for director, and whether your shares should be voted for, against or abstain with respect to the other proposal. If you properly submit a proxy without giving specific voting instructions, your shares will be voted in accordance with the Board’s recommendations as noted below. Voting by proxy will not affect your right to attend the annual meeting. If your shares are registered directly in your name through our stock transfer agent, Equiniti Trust Company, LLC, or you have stock certificates registered in your name, you may vote:

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By Internet or by telephone. Follow the instructions included in the Notice or, if you received printed materials, in the proxy card to vote over the Internet or by telephone.

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By mail. If you received a proxy card by mail, you can vote by mail by completing, signing, dating and returning the proxy card as instructed on the card. If you sign the proxy card but do not specify how you want your shares voted, they will be voted in accordance with the Board’s recommendations as noted below.

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At the time of the virtual Annual Meeting. If you attend the virtual Annual Meeting, you may vote your shares online at the time of the meeting.

Telephone and Internet voting facilities for stockholders of record will be available 24 hours a day and will close at 11:59 p.m. Eastern Time on December 14, 2025.

If your shares are held in “street name” (held in the name of a bank, broker or other holder of record), you will receive instructions from the holder of record. You must follow the instructions of the holder of record in order for your shares to be voted. Telephone and Internet voting also will be offered to stockholders owning shares through certain banks and brokers. If your shares are not registered in your own name and you plan to vote your shares at the time of the virtual annual meeting, you should contact your broker or agent to obtain a legal proxy or broker’s proxy card and vote your shares online at the time of the meeting.

How Does the Board Recommend That I Vote on the Proposals?

The Board recommends that you vote as follows:

•

“FOR” the election of the nominees for director;

•

“FOR” the advisory vote to approve the compensation of the Company’s named executive officers, as disclosed in this proxy statement;

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“FOR” the approval of the Synlogic, Inc. 2025 Equity Incentive Plan; and

•

“FOR” the ratification of the selection of KPMG LLP as our independent registered public accounting firm for our fiscal year ending December 31, 2025.

If any other matter is presented at the annual meeting, your proxy provides that your shares will be voted by the proxy holder listed in the proxy in accordance with his or her best judgment. At the time this proxy statement was first made available, we knew of no matters that needed to be acted on at the annual meeting, other than those discussed in this proxy statement.

May I Change or Revoke My Proxy?

If you give us your proxy, you may change or revoke it at any time before the annual meeting. You may change or revoke your proxy in any one of the following ways:

•

if you received a proxy card, by signing a new proxy card with a date later than your previously delivered proxy and submitting it as instructed above;

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by re-voting by Internet or by telephone as instructed above;

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by notifying Synlogic’s Corporate Secretary in writing before the annual meeting that you have revoked your proxy; or

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by attending the virtual annual meeting and voting online at the time. Attending the virtual annual meeting will not in and of itself revoke a previously submitted proxy. You must specifically request at the virtual annual meeting that it be revoked.

Your most current vote, whether by telephone, Internet or proxy card is the one that will be counted.

What if I Receive More Than One Proxy Card?

You may receive more than one proxy card if you hold shares of our common stock in more than one account, which may be in registered form or held in street name. Please vote in the manner described above under “How Do I Vote?” for each account to ensure that all of your shares are voted.

Will My Shares be Voted if I Do Not Vote?

If your shares are registered in your name or if you have stock certificates, they will not be counted if you do not vote as described above under “How Do I Vote?” If your shares are held in street name and you do not provide voting instructions to the bank, broker or other nominee that holds your shares as described above, the bank, broker or other nominee that holds your shares has the authority to vote your unvoted shares only with respect to Proposal 4. Therefore, we encourage you to provide voting instructions to your bank, broker or other nominee. This ensures your shares will be voted at the annual meeting and in the manner you desire. A “broker non-vote” will occur if your broker cannot vote your shares on a particular matter because it has not received instructions from you and does not have discretionary voting authority on that matter or because your broker chooses not to vote on a matter for which it does have discretionary voting authority.

What Vote is Required to Approve Each Proposal and How are Votes Counted?


Proposal 1: Elect Directors		The nominees for director who receives the most votes (also known as a “plurality” of the votes cast) will be elected. You may vote either FOR the nominees or WITHHOLD your vote from the nominees. Votes that are withheld will not be included in the vote tally for the election of the director. Brokerage firms do not have authority to vote customers’ unvoted shares held by the firms in street name for the election of directors. As a result, any shares not voted by a customer will be treated as a broker non-vote. Such broker non-votes will have no effect on the results of this vote.
Proposal 2: Advisory vote on Executive Compensation		For the advisory vote on executive compensation, the votes cast FOR must exceed the votes cast AGAINST to approve, on an advisory basis, the compensation of our named executive officers. Only FOR and AGAINST votes will affect the outcome. Abstentions will have no effect on the voting of Proposal 2. Therefore, if your shares are held by your bank, broker or other nominee in street name and you do not vote your shares, your bank, broker or other nominee cannot vote your shares on Proposal 2. Shares held in street name by banks, brokers or nominees who indicate on their proxies that they do not have authority to vote the shares on Proposal 2 will not be counted as votes FOR or AGAINST the proposal and will be treated as broker non-votes. As a result, broker non-votes will have no effect on the results of this vote. Although the advisory vote is non-binding, the Compensation Committee and the Board of Directors will review the voting results and take them into consideration when making future decisions regarding executive compensation.

Proposal 3: Approval of Adoption of Synlogic, Inc.'s 2025 Equity Incentive Plan		The affirmative vote of a majority of the shares cast affirmatively or negatively for this proposal is required for the approval of the Plan. Only FOR and AGAINST votes will affect the outcome. Abstentions will have no effect on the results of this vote. Brokerage firms do not have authority to vote customers’ unvoted shares held by the firms in street name on this proposal. As a result, any shares not voted by a customer will be treated as a broker non-vote. Such broker non-votes will have no effect on the results of this vote.

Proposal 4: Ratify Selection of Independent Registered Public Accounting Firm		The affirmative vote of a majority of the shares cast affirmatively or negatively for this proposal is required to ratify the selection of our independent registered public accounting firm. Abstentions will have no effect on the results of this vote. Brokerage firms have authority to vote customers’ unvoted shares held by the firms in street name on this proposal. If a broker does not exercise this authority, such broker non-votes will have no effect on the results of this vote. We are not required to obtain the approval of our stockholders to select our independent registered public accounting firm. However, if our stockholders do not ratify the selection of KPMG LLP as our independent registered public accounting firm for 2025, our Audit Committee of our Board will reconsider its selection.

Is Voting Confidential?

We will keep all the proxies, ballots and voting tabulations private. We only let our Inspector of Elections examine these documents. Management will not know how you voted on a specific proposal unless it is necessary to meet legal requirements. We will, however, forward to management any written comments you make on the proxy card or otherwise provide.

Where Can I Find the Voting Results of the Annual Meeting?

The preliminary voting results will be announced at the Annual Meeting, and we will publish preliminary results, or final results if available, in a Current Report on Form 8-K within four business days of the annual meeting. If final results are unavailable at the time we file the Form 8-K, then we will file an amended report on Form 8-K to disclose the final voting results within four business days after the final voting results are known.

What Are the Costs of Soliciting these Proxies?

We will pay all of the costs of soliciting these proxies. Our directors and employees may solicit proxies in person or by telephone, fax or email. We will pay these employees and directors no additional compensation for these services. We will ask banks, brokers and other institutions, nominees and fiduciaries to forward these proxy materials to their principals and to obtain authority to execute proxies. We will then reimburse them for their expenses.

What Constitutes a Quorum for the Annual Meeting?

The presence, in person or by proxy, of the holders of a majority of the voting power of all outstanding shares of our common stock entitled to vote at the annual meeting is necessary to constitute a quorum at the annual meeting. Votes of stockholders of record who are present at the annual meeting in person or by proxy, abstentions, and broker non-votes are counted for purposes of determining whether a quorum exists.

Attending the Annual Meeting

This year, we will host our Annual Meeting at 9:00 a.m. Eastern time on December 15, 2025. You will be able to participate in the Annual Meeting, vote your shares electronically and submit your questions during the live webcast of the meeting by visiting www.virtualshareholdermeeting.com/SYBX2025 and entering your 16-digit control number found on the enclosed voting form. You need not attend the Annual Meeting in order to vote.

Householding of Annual Disclosure Documents

SEC rules concerning the delivery of annual disclosure documents allow us or your broker to send a single Notice or, if applicable, a single set of our proxy materials to any household at which two or more of our stockholders reside, if we or your broker believe that the stockholders are members of the same family. This practice, referred to as “householding,” benefits both you and us. It reduces the volume of duplicate information received at your household and helps to reduce our expenses. The rule applies to our Notices, annual reports, proxy statements and information statements. Once you receive notice from your broker or from us that communications to your address will be “householded,” the practice will continue until you are otherwise notified or until you revoke your consent to the practice. Stockholders who participate in householding will continue to have access to and utilize separate proxy voting instructions.

If your household received a single set of proxy materials this year, but you would prefer to receive your own copy, please contact our Corporate Secretary at Synlogic, Inc., PO Box 30, Winchester, MA 01890.

If you do not wish to participate in “householding” and would like to receive your own set of Synlogic’s proxy materials in future years, follow the instructions described below.

Conversely, if you share an address with another Synlogic stockholder and together both of you would like to receive only a single set of proxy materials, follow these instructions:

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If your Synlogic shares are registered in your own name, please contact our transfer agent, Equiniti Trust Company, LLC, and inform them of your request by calling them at 1-800-937-5449 or writing them at 6201 15th Avenue, Brooklyn, NY 11219.

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If a broker or other nominee holds your Synlogic shares, please contact the broker or other nominee directly and inform them of your request. Be sure to include your name, the name of your brokerage firm and your account number.

Electronic Delivery of Company Stockholder Communications

Most stockholders can elect to view or receive copies of future proxy materials over the Internet instead of receiving paper copies in the mail.

You can choose this option and save the Company the cost of producing and mailing these documents by:

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following the instructions provided on your proxy card; or

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following the instructions provided when you vote over the Internet.

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

The following table sets forth certain information with respect to the beneficial ownership of our common stock as of October 31, 2025 for (a) the executive officers named in the Summary Compensation Table on page 15 of this proxy statement, (b) each of our directors and director nominees, (c) all of our current directors and executive officers as a group and (d) each stockholder known by us to own beneficially more than 5% of our common stock. Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to the securities. We deem shares of common stock that may be acquired by an individual or group within 60 days of October 31, 2025 pursuant to the exercise of options to be outstanding for the purpose of computing the percentage ownership of such individual or group, but are not deemed to be outstanding for the purpose of computing the percentage ownership of any other person shown in the table. Except as indicated in footnotes to this table, we believe that the stockholders named in this table have sole voting and investment power with respect to all shares of common stock shown to be beneficially owned by them based on information provided to us by these stockholders. Percentage of ownership is based on 11,698,919 shares of common stock outstanding on October 31, 2025.


	Shares Beneficially
	Owned (1)
	Number		Percent
Name and Address of Beneficial Owner**
Directors and Named Executive Officers:
Peter Barrett, Ph.D. (2)		232,842		1.98	%
Aoife Brennan, MB, BCh, BAO, MMSc (3)		111,895	*
Antoine Awad (4)		69,288	*
Mary Beth Dooley (5)		25,664	*
Richard P. Shea (6)		23,970
James Flynn (7)		16,333	*
Edward Mathers (8)		8,465	*
All current directors and executive officers as a group (5 persons) (9)		307,274		2.62

SEC Form DEF 14A filed by Synlogic Inc.