ALNYLAM 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:

☐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 Pursuant to §240.14a-12

Alnylam 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):

☑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.

Letter from our CEO

March 24, 2025

To our Stockholders:

We invite you to attend the 2025 Annual Meeting of Stockholders of Alnylam Pharmaceuticals, Inc., which will be held online on Thursday, May 8, 2025, beginning at 8:30 a.m., Eastern Time. You may attend the meeting virtually via the Internet atwww.virtualshareholdermeeting.com/ALNY2025, where you will be able to vote electronically and submit questions. You will need the 16-digit control number included with these proxy materials to attend the annual meeting.

The following notice of our annual meeting of stockholders contains details of the business to be conducted at the meeting. Only stockholders of record at the close of business on March 10, 2025 will be entitled to notice of, and to vote at, the annual meeting.

On behalf of our Board of Directors, thank you for your continued support of Alnylam.

Very truly yours,

YVONNE L. GREENSTREET, M.D.

Chief Executive Officer and Director

On behalf of the Board of Directors of Alnylam Pharmaceuticals, Inc.

Notice of 2025 Annual Meeting of Stockholders

Voting

Proposal 1 relates solely to the election of four (4) Class III directors nominated by our board of directors and does not include any other matters relating to the election of directors, including without limitation, the election of directors nominated by any stockholder of the company.

Your vote is important regardless of the number of shares you own. Whether or not you plan to participate in the annual meeting online, we hope you will take the time to vote your shares. To ensure your representation at the annual meeting, if you are a stockholder of record, please vote in one of these three ways:

If you choose to vote your shares by mail or by telephone or Internet in advance of the meeting, your vote must be received by 11:59 p.m., Eastern Time on May 7, 2025 to be counted.

If you vote via the Internet or by telephone in advance of the meeting or if you mail your proxy in, you will not limit your right to vote online at the annual meeting. If your shares are held in “street name,” that is, held for your account by a broker or other nominee, you will receive instructions from the holder of record that you must follow for your shares to be voted.

Notice of 2025 Annual Meeting of Stockholders

By Order of the Board of Directors,Robert W. HessleinExecutive Vice President, Chief Legal Officer and SecretaryCambridge, MassachusettsMarch 24, 2025

IMPORTANT NOTICE REGARDING THE INTERNET AVAILABILITY OF PROXY MATERIALS FOR THE STOCKHOLDER MEETING TO BE HELD ON MAY 8, 2025This Notice of 2025 Annual Meeting, Proxy Statement, 2024 Annual Report on Form 10-K and Annual Report to Stockholders are available for viewing, printing and downloading at www.proxyvote.com.

Notice of 2025 Annual Meeting of Stockholders

Cautionary Note Regarding Forward-Looking Statements

This proxy statement contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. All statements other than historical statements of fact regarding Alnylam’s expectations, beliefs, goals, plans or prospects including, without limitation, statements regarding Alnylam’s expectations with respect to its “Alnylam P 5 x25” goals; the company’s projected commercial and financial performance; the anticipated timelines and progress with respect to the company’s environmental sustainability, corporate responsibility and environmental, social and governance initiatives; the company’s commitments and progress pursuant to its Patient Access Philosophy; and the company’s plans with respect to stockholder engagement, should be considered forward-looking statements. Actual results and future plans may differ materially from those indicated by these forward-looking statements as a result of various important risks, uncertainties and other factors, including, without limitation, risks and uncertainties relating to: Alnylam’s ability to successfully execute on its “Alnylam P 5 x25” strategy; Alnylam’s ability to discover and develop novel drug candidates and delivery approaches and successfully demonstrate the efficacy and safety of its product candidates; the pre-clinical and clinical results for Alnylam’s product candidates, including vutrisiran, zilebesiran, nucresiran and mivelsiran; actions or advice of regulatory agencies and Alnylam’s ability to obtain and maintain regulatory approval for its product candidates, as well as favorable pricing and reimbursement; successfully launching, marketing and selling Alnylam’s approved products globally; delays, interruptions or failures in the manufacture and supply of Alnylam’s product candidates or its marketed products; obtaining, maintaining and protecting intellectual property; Alnylam’s ability to successfully expand the approved indications for AMVUTTRA in the future; Alnylam’s ability to manage its growth and operating expenses through disciplined investment in operations and its ability to achieve a self-sustainable financial profile; Alnylam’s ability to maintain strategic business collaborations; Alnylam’s dependence on third parties for the development and commercialization of certain products; the outcome of litigation; the risk of government investigations; and unexpected expenditures; as well as those risks and uncertainties more fully discussed in the “Risk Factors” filed with Alnylam’s most recent Annual Report on Form 10-K filed with the Securities and Exchange Commission, or SEC, on February 13, 2025, as may be updated from time to time in other filings that Alnylam makes with the SEC. In addition, any forward-looking statements represent Alnylam’s views only as of the date of this proxy statement and should not be relied upon as representing its views as of any subsequent date. Alnylam explicitly disclaims any obligation, except to the extent required by law, to update any forward-looking statements.