RAPID MICRO BIOSYSTEMS, INC.

25 HARTWELL AVENUE, LEXINGTON, MASSACHUSETTS 02421

This proxy statement is furnished in connection with the solicitation by the Board of Directors (the “Board of Directors” or the “Board”) of Rapid Micro Biosystems, Inc. of proxies to be voted at our Annual Meeting of Stockholders to be held on Thursday, May 21, 2026 (“Annual Meeting” or “Annual Meeting”), at 9:00 a.m., Eastern Time, and at any continuation, postponement, or adjournment of the Annual Meeting. The Annual Meeting will be conducted virtually via live webcast. You will be able to attend the Annual Meeting, vote electronically and submit your questions during the Annual Meeting by visiting www.virtualshareholdermeeting.com/RPID2026 and entering the 16-digit control number included in your Notice of Internet Availability of Proxy Materials ("Notice of Internet Availability"), on your proxy card or on the instructions that accompanied your proxy materials.

Only holders of record of outstanding shares of our Class A common stock (our “Class A stockholders”) at the close of business on March 31, 2026 (the “Record Date”) will be entitled to notice of, and to vote at, the Annual Meeting and any continuation, postponement, or adjournment of the Annual Meeting. Each share of our Class A common stock entitles its holder to one vote on all matters presented to our stockholders. At the close of business on the Record Date, there were 41,267,511 shares of Class A common stock outstanding and entitled to vote at the Annual Meeting. The holders of our Class B common stock are not entitled to notice of, or to vote on, any matter before the Annual Meeting.

Even if you plan to attend the Annual Meeting online, we encourage you to vote in advance of the Annual Meeting as described in this proxy statement, so that your vote will be counted if you later decide not to attend the Annual Meeting or encounter technical difficulties. If you wish to submit your vote before the Annual Meeting, then you do not have to vote at the Annual Meeting unless you wish to change your vote.

If you do not have a 16-digit control number, you may still attend the Annual Meeting as a guest in listen-only mode. To attend as a guest, please visit www.virtualshareholdermeeting.com/RPID2026 and enter the information requested on the screen to register as a guest. Please note that you will not have the ability to vote or ask questions during the meeting if you participate as a guest.

This proxy statement, form of proxy card and the Company’s 2025 Annual Report to stockholders for the fiscal year ended December 31, 2025 (the “2025 Annual Report”) were first made available to stockholders on or about April 8, 2026 to our Class A stockholders as of the Record Date.

In this proxy statement, “we,” “us,” “our,” the “Company” and “Rapid Micro Biosystems” refer to Rapid Micro Biosystems, Inc., and, unless otherwise stated, all of its subsidiaries.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS

FOR THE ANNUAL MEETING TO BE HELD ON THURSDAY, MAY 21, 2026

This Proxy Statement and our 2025 Annual Report,

which includes our Annual Report on Form 10-K for the fiscal year ended December 31, 2025,

are available at http://www.proxyvote.com/

and at investors.rapidmicrobio.com under the tab “Financial Information”

for viewing, downloading and printing.

A copy of our Annual Report on Form 10-K for the year ended December 31, 2025 as filed with the Securities and Exchange Commission (the "SEC"), except for exhibits, will be furnished without charge to any stockholder upon written or oral request to Rapid Micro Biosystems, Inc., 25 Hartwell Avenue, Lexington, Massachusetts 02421, Attention: Investor Relations, Telephone 1-978-349-3200.

To attend, vote and submit questions during the Annual Meeting visit www.virtualshareholdermeeting.com/RPID2026 and enter the control number included in your Notice of Internet Availability, voting instruction form, or proxy card. Stockholders may vote during the Annual Meeting by following the instructions available on the Annual Meeting website. Those without a control number may attend as guests of the meeting but will not have the option to vote or ask questions during the virtual meeting. Online access to the webcast will open approximately 15 minutes prior to the start of the Annual Meeting. To submit questions in advance of the Annual Meeting, visit www.proxyvote.com before noon Eastern Time on May 20, 2026 and enter your control number.

All stockholders—even if you plan on attending the Annual Meeting—are encouraged to vote their shares in advance online or, if you requested printed copies of the proxy materials, by phone or by mail, to ensure that your vote will be represented at the Annual Meeting. For more detailed information, see the section entitled “How Do I Vote” beginning on page 5 of this proxy statement.

Proxy Materials Are Available on the Internet

Rapid Micro Biosystems uses the Internet as the primary means of furnishing proxy materials to stockholders. We send a Notice of Internet Availability to our stockholders with instructions on how to access the proxy materials online at proxyvote.com or request a printed copy of materials.

Stockholders may follow the instructions in the Notice of Internet Availability to elect to receive future proxy materials in print by mail or electronically by email. We encourage stockholders to take advantage of the availability of proxy materials online to reduce environmental impact and mailing costs.

Rapid Micro Biosystems’ proxy materials are also available at investors.rapidmicrobio.com.