X0306 4 2021-03-29 0 0001643615 Montrose Environmental Group, Inc. MEG 0001817948 Manthripragada Vijay 1 PARK PLAZA, SUITE 1000 IRVINE CA 92614 1 1 0 0 President and CEO Common Stock 2021-03-29 4 M 0 72027 6.03 A 84955 D Common Stock 2021-03-29 4 S 0 39968 43.679 D 44987 D Common Stock 2021-03-29 4 S 0 32059 44.156 D 12928 D Stock Option (Right to Buy) 6.03 2021-03-29 4 M 0 72027 0.00 D 2026-06-23 Common Stock 72027 554098 D The price reported in Column 4 is a weighted average price. These shares of common stock of the Issuer were sold in multiple transactions by the Reporting Person at prices ranging from $42.98 to $43.975, inclusive. The Reporting Person undertakes to provide upon request by the Commission staff, the Issuer, or a security holder of the Issuer full information regarding the number of shares of common stock sold at each separate price within the range. The price reported in Column 4 is a weighted average price. These shares of common stock of the Issuer were sold in multiple transactions by the Reporting Person at prices ranging from $43.98 to $44.37, inclusive. The Reporting Person undertakes to provide upon request by the Commission staff, the Issuer, or a security holder of the Issuer full information regarding the number of shares of common stock sold at each separate price within the range. 50% of the shares subject to the option vested on September 11, 2017, and the remaining 50% vested on September 11, 2019. The transactions reported in this Form 4 were effected pursuant to a Rule 10b5-1 Trading Plan adopted by the Reporting Person. /s/ Nasym Afsari, Attorney in fact 2021-03-31