Exhibit 3.1

CERTIFICATE OF AMENDMENT

OF

AMENDED AND RESTATED CERTIFICATE OF INCORPORATION

OF

MONTROSE ENVIRONMENTAL GROUP, INC.

Pursuant to Section 242

of the General Corporation Law of the State of Delaware

MONTROSE ENVIRONMENTAL GROUP, INC., a corporation duly organized and existing under the General Corporation Law of the State of Delaware (the “DGCL”), does hereby certify:

FIRST: That the name of the corporation is Montrose Environmental Group, Inc. (the “Corporation”), and that the Corporation was originally incorporated pursuant to the DGCL on November 25, 2013.

SECOND: The Corporation’s Certificate of Incorporation was filed with the Secretary of State of the State of Delaware on November 25, 2013, and subsequently amended by that certain Certificate of Amendment of Certificate of Incorporation dated December 6, 2017, and that certain Certificate of Amendment of Certificate of Incorporation dated April 13, 2020.

THIRD: That the Certificate of Incorporation of the Corporation, as amended as of such date, was amended and restated in the form filed with the Secretary of Sate of the State of Delaware on July 21, 2020 (as so amended and restated, the “Amended and Restated Certificate of Incorporation”).

FOURTH: That the Amended and Restated Certificate of Incorporation is hereby amended as follows:

A.Section 5.2 of Article V is hereby amended to read in its entirety as follows:

Section 5.2 Classification.

(a) Except as may be otherwise provided with respect to directors elected by the holders of any series of Preferred Stock provided for or fixed pursuant to the provisions of Article IV hereof (including any Preferred Stock Designation) (the “Preferred Stock Directors”), the Board of Directors shall be divided into three classes, as nearly equal in number as possible, designated Class I, Class II and Class III. Class I directors shall initially serve until the first annual meeting of stockholders following the initial effectiveness of this Section 5.2; Class II directors shall initially serve until the second annual meeting of stockholders following the initial effectiveness of this Section 5.2; and Class III directors shall initially serve until the third annual meeting of stockholders following the initial effectiveness of this Section 5.2. Commencing with the first annual meeting of stockholders following the initial effectiveness of this Section 5.2, directors of each class the term of which shall then expire shall be elected to hold office for a three-year term and until the election and qualification of their respective successors in office. In case of any increase or decrease, from time to time, in the number of directors (other than Preferred Stock Directors), the number of

directors in each class shall be apportioned as nearly equal as possible. The Board of Directors is authorized to assign members of the Board of Directors already in office to Class I, Class II or Class III, with such assignment becoming effective as of the initial effectiveness of this Section 5.2.

(b) Subject to the rights of the holders of any outstanding series of Preferred Stock, and unless otherwise required by law, newly created directorships resulting from any increase in the authorized number of directors and any vacancies in the Board of Directors resulting from death, resignation, retirement, disqualification, removal from office or other cause shall be filled solely by the affirmative vote of a majority of the remaining directors then in office, even though less than a quorum of the Board of Directors, or by the sole remaining director. Any director so chosen shall hold office until the next election of the class for which such director shall have been chosen and until his or her successor shall have been duly elected and qualified. No decrease in the authorized number of directors shall shorten the term of any incumbent director.

(c) Any director, or the entire Board of Directors, may be removed from office at any time, but only for cause and only by the affirmative vote of at least a majority of the voting power of the stock outstanding and entitled to vote thereon.

B.Sections 10.1 and 10.2 of Article X are hereby amended to read in their entirety as follows:

Section 10.1 Amendment of Certificate of Incorporation. The Corporation reserves the right at any time, and from time to time, to amend, alter, change or repeal any provision contained in this Certificate of Incorporation (including any Preferred Stock Designation), and other provisions authorized by the laws of the State of Delaware at the time in force may be added or inserted, in the manner now or hereafter prescribed by the laws of the State of Delaware, and all powers, preferences and rights of any nature conferred upon stockholders, directors or any other persons by and pursuant to this Certificate of Incorporation (including any Preferred Stock Designation) in its present form or as hereafter amended are granted subject to this reservation.

Section 10.2 Amendment of Bylaws. In furtherance and not in limitation of the powers conferred by the laws of the State of Delaware, but subject to the terms of any series of Preferred Stock then outstanding, the Board of Directors is expressly authorized to adopt, amend or repeal the Bylaws of the Corporation. Except as otherwise provided in this Certificate of Incorporation (including the terms of any Preferred Stock Designation that require an additional vote) or the Bylaws of the Corporation, and in addition to any requirements of law, the affirmative vote of at least a majority of the voting power of the stock outstanding and entitled to vote thereon, voting together as a single class, shall be required for the stockholders to adopt, amend or repeal, or adopt any provision inconsistent with, any provision of the Bylaws of the Corporation.

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FIFTH: That the foregoing amendments to the Amended and Restated Certificate of Incorporation were duly adopted in accordance with the provisions of Section 242 of the DGCL.

[Signature Page Follows]

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IN WITNESS WHEREOF, the Corporation has caused this Certificate of Amendment to be executed by a duly authorized officer on the date set forth below.

MONTROSE ENVIRONMENTAL GROUP, INC.

By: /s/ Nasym Afsari____________

Name: Nasym Afsari

Title: General Counsel and Secretary

Dated: May 10, 2024

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