[9] In 2019, he began the season with the Columbia Fireflies and earned promotions to the St. Lucie Mets and the Binghamton Rumble Ponies during the year.

[15] On July 23, Megill earned his first major league win after pitching six shutout innings against the Toronto Blue Jays.

[18] At the start of the 2022 season, Megill was named the team's Opening Day starter due to injuries to Jacob deGrom and Max Scherzer.

[22] He was placed on the COVID-19 injured list shortly before the final game of the regular season and two days before the start of the team's playoff series against the San Diego Padres.

[citation needed] Megill was named the Mets' fifth starter entering the 2024 season after beating out José Butto in spring training.

[25] On August 2, Megill was sent to Triple-A as Paul Blackburn made his first start for the Mets; previously, he was used in the bullpen for the July 31 game against the Minnesota Twins.

[26] However, Megill was called back up ahead of the August 30 game against the Chicago White Sox, earning his first win since June 16.