Ameresco 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 Registrantþ

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))

þ Definitive Proxy Statement

¨ Definitive Additional Materials

¨ Soliciting Material under §240.14a-12

Ameresco, 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):

þ No fee required.

¨ Fee paid previously with preliminary materials

¨ Fee computed on table below per Exchange Act Rules 14a-6(i)(1) and 0-11.

NOTICE OF 2025 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 4, 2025

To Our Stockholders:

The 2025 annual meeting of stockholders of Ameresco, Inc., a Delaware corporation, will be held on June 4, 2025, at 10:00 a.m., Eastern Time, for the following purposes:

1. To elect thetwo (2) nominees identified in the accompanying proxy statement as members of our board of directors to serve as class III directors for a term of three years.

2. To ratify the appoi ntment of RSM US LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2025.

3. To approve an amendment to our Restated Certificate of Incorporation to reflect new Delaware law provisions regarding officer exculpation; and

4. To transact other busi ness, if any, that may properly come before the annual meeting and any adjournment thereof.

The foregoing items of business are more fully described in the Proxy Statement. Only stockholders who owned our Class A common stock or Class B common stock at the close of business on April 10, 2025, can vote at the Annual Meeting or any adjournments or postponements that take place.

Our board of directors, or board, recommends that you vote FOR the election of the director nominees named in Proposal 1, FORthe ratification of the appointment of RSM US LLP as our independent registered public accounting firm as described in Proposal 2, and FOR the approval of an amendment to Ameresco Inc.’s Restated Certificate of Incorporation to reflect new Delaware law provisions regarding officer exculpation as described in Proposal 3.

This year’s annual meeting will be a completely virtual meeting of stockholders, conducted via an online platform. The Annual Meeting can be accessed by visiting www.virtualshareholdermeeting.com/AMRC2025, where you will be able to listen to the meeting live, submit questions and vote online.

We are pleased to utilize the Securities and Exchange Commission, or SEC, rules that allow issuers to furnish proxy materials to their stockholders on the Internet. On or about April 24, 2025, we will mail to our stockholders of record as of April 10, 2025 (other than those who previously requested electronic or paper delivery on an ongoing basis) a Notice Regarding the Availability of Proxy Materials, or Notice, with instructions for accessing the proxy materials and voting over the Internet, by telephone or mobile device or by mail. The Notice also provides information on how stockholders may request paper copies of our proxy materials. We believe electronic delivery of our proxy materials and our 2024 Annual Report will help us reduce the environmental impact and costs of printing and distributing paper copies and improve the speed and efficiency by which our stockholders can access these materials.

Your vote is very important. Whether or not you plan to attend the virtual annual meeting, we encourage you to read our proxy materials and submit your proxy or voting instructions as soon as possible over the Internet, by telephone or mobile device or by mail.

By Order of the Board of Directors,

David J. Corrsin

Secretary

April 24, 2025

TABLE OF CONTENTS

AMERESCO, INC.

111 Speen Street, Suite 410,

Framingham, Massachusetts 01701

PROXY STATEMENT FOR 2025 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 4, 2025