RHYTHM PHARMACEUTICALS 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.)

Filed by the Registrant☒

Filed by a Party other than the Registrant☐

Check the appropriate box:

RHYTHM PHARMACEUTICALS, 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 all boxes that apply):

April 29, 2025

Dear Stockholder:

On behalf of the Board of Directors of Rhythm Pharmaceuticals, Inc. (the “Company,” “we” or “Rhythm”), I invite you to attend the Annual Meeting of Stockholders (the “Annual Meeting”) that will be held on Tuesday, June 24, 2025, at 2:00 p.m., Eastern Time. The Annual Meeting will be held entirely online. You will be able to attend the Annual Meeting online and submit your questions during the meeting by visiting*www.meetnow.global/*MSGDG5G. The matters to be voted upon at the Annual Meeting are listed in the Notice of Annual Meeting of Stockholders and more fully described in the definitive proxy statement accompanying this letter (the “Proxy Statement”).

All stockholders of record of our common stock, $0.001 par value per share, (the “Common Stock”) and Series A Convertible Preferred Stock, $0.001 par value per share (“Convertible Preferred Stock”) at the close of business on April 28, 2025, the record date, are entitled to notice of the Annual Meeting and any continuation, postponement, or adjournment thereof. Stockholders of record of our Common Stock are entitled to vote at the Annual Meeting. Holders of our Convertible Preferred Stock are entitled to vote at the Annual Meeting, subject to the terms of the Convertible Preferred Stock as specified in the Amended and Restated Certificate of Designations for the Convertible Preferred Stock (the “Certificate of Designations”). For more information, see “Who can vote at the Annual Meeting?” on page 1 of the accompanying Proxy Statement.

We know that certain of our stockholders will be unable to attend the Annual Meeting electronically. We, therefore, are soliciting proxies so that each stockholder has an opportunity to vote on the matters that are scheduled to come before the stockholders at the Annual Meeting. If you have previously received our Notice of Internet Availability of Proxy Materials (the “Internet Notice”), then instructions regarding how you can vote are contained in that notice. If you have received a proxy card, then instructions regarding how you can vote are contained on the proxy card. Submitting your vote via the Internet or by telephone or proxy card will not affect your right to vote electronically if you decide to attend the Annual Meeting. If your shares are held in street name (held for your account by a broker or other nominee), you will receive instructions from your broker or other nominee explaining how to vote your shares. Whether or not you expect to attend the Annual Meeting electronically, we urge you to vote your shares as promptly as possible to ensure your representation and the presence of a quorum at the Annual Meeting. Your proxy is revocable in accordance with the procedures set forth in the Proxy Statement.

Thank you for your continuing interest in the Company.

NOTICE OF ANNUAL MEETING OF STOCKHOLDERS

The Annual Meeting of Stockholders (the “Annual Meeting”) of Rhythm Pharmaceuticals, Inc. (the “Company,” “we” or “Rhythm”) will be held on Tuesday, June 24, 2025, at 2:00 p.m., Eastern Time. The Annual Meeting will be a completely virtual meeting, which will be conducted via live webcast. You will be able to attend the Annual Meeting online and submit your questions during the meeting by visitingwww.meetnow.global/MSGDG5G and entering the control number included in your Notice of Internet Availability of Proxy Materials (the “Internet Notice”), on any proxy card that you received or on the instructions that accompanied your proxy materials. The Annual Meeting will be held for the following purposes:

The Board has fixed the close of business on April 28, 2025 as the record date for determining stockholders entitled to notice of and to vote at the Annual Meeting. To participate in the Annual Meeting, including to vote via the Internet or telephone, you will need the control number included in your Internet Notice, on any proxy card that you received or on the instructions that accompanied your proxy materials. A complete list of such stockholders will be open to the examination of any stockholder for a period of ten days prior to the Annual Meeting for a purpose germane to the meeting by sending an email to David Connolly, Head of Investor Relations and Corporate Communications, at dconnolly@rhythmtx.com, stating the purpose of the request and providing proof of ownership of Company stock. The Annual Meeting may be continued or adjourned from time to time without notice other than by announcement at the Annual Meeting.

Whether or not you expect to attend the Annual Meeting electronically, we urge you to vote your shares as promptly as possible to ensure your representation and the presence of a quorum at the Annual Meeting. If you choose to attend the Annual Meeting, you may still vote your shares electronically, even if you have previously voted or returned your proxy by any of the methods described in the Proxy Statement. If your shares are held in street name in a bank or brokerage account, please refer to the materials provided by your bank, broker or other nominee for voting instructions. Your proxy is revocable in accordance with the procedures set forth in the Proxy Statement.

All stockholders are extended a cordial invitation to attend the meeting online.