The Mets signed Montas to a two-year, $34 million contract Sunday, Jeff Passan of ESPN.com reports.
Montas declined his portion of a $20 million mutual option for 2025, Adam McCalvy of MLB.com reports.
Montas will start Game 2 of the Brewers' wild-card series against the Mets on Wednesday, Adam McCalvy of MLB.com reports.
Montas surrendered eight runs (seven earned) on six hits and two walks over 2.2 innings during Sunday's win against the Diamondbacks. He struck out four and did not factor in the decision.
Montas (7-11) took the loss Tuesday as the Brewers were downed 5-1 by the Phillies, giving up three runs on six hits and two walks over 5.2 innings. He struck out 10.
Montas (7-10) picked up the win over the Giants on Thursday, allowing two hits and two walks over six scoreless frames while striking out eight.
Montas (6-8) picked up the win in Tuesday's 3-2 victory over the Cardinals, allowing one hit and one walk over seven scoreless innings. He struck out three.
Montas did not factor into the decision in a win over the Dodgers on Wednesday, allowing three unearned runs on five hits and three walks over five innings while striking out six.
Montas allowed three runs on two hits and four walks over four innings during Thursday's 16-7 win against Atlanta. He struck out seven and did not factor in the decision.
Montas (5-8) picked up the win Friday, giving up three runs on nine hits over five innings in an 8-3 victory over the Nationals. He struck out five without walking a batter.