On July 31, 2018, Zimmermann, Jean Carlos Encarnacion, Brett Cumberland, Evan Phillips and international signing money were traded to the Baltimore Orioles in exchange for Kevin Gausman and Darren O'Day.[8] He was assigned to the Double-A Bowie Baysox and finished the season there. In 25 starts between Rome, Mississippi, and Bowie, he compiled an 11–7 record with a 3.21 ERA.[9] He returned to Bowie to begin 2019[10] before being promoted to the Triple-A Norfolk Tides in July.[11][12] Over 25 games (24 starts) between the two clubs, Zimmermann pitched to a 7–6 record with a 3.21 ERA, striking out 134 over 140 innings.[13]
His addition to the Orioles' 60-player Alternate Training Site pool was delayed to August 2020 due to his recovery from COVID-19. Hours after he was added to the team's 40-man roster when his contract was selected by the Orioles, Zimmermann pitched three innings as the starting pitcher in his MLB debut in a 10–6 loss to the Tampa Bay Rays in the second game of a two-night doubleheaderatCamden Yards on September 17, 2020.[14] Zimmermann gave up six earned runs over seven innings pitched in his debut season in 2020.[15]
On August 15, 2021, Zimmermann was placed on the 60-day injured list. Zimmermann had been nearing a return to the team from biceps tendinitis but suffered a sprained right ankle.[16] He was activated from the injured list on September 28. On the season, he went 4-5 with a 5.04 ERA and 56 strikeouts in 64.1 innings pitched across 14 games (13 starts).
In 2022, Zimmermann made 15 appearances (13 starts) for Baltimore. In 73.2 innings pitched, he recorded a 2-5 record with a 5.99 ERA and 49 strikeouts. On June 16, 2022, he was optioned to Norfolk after allowing six runs in 4.2 innings pitched against the Toronto Blue Jays.[17]
Zimmermann was optioned to Triple-A Norfolk to begin the 2023 season.[18] On June 13, 2023, while pitching for Norfolk, Zimmermann tossed a complete–game shutout against the Worcester Red Sox.[19] He pitched in just seven games for Baltimore, logging a 4.73 ERA with 14 strikeouts in 13+1⁄3 innings of work. Following the season on October 19, Zimmermann underwent core muscle surgery.[20]
Zimmermann was optioned to Triple–A Norfolk to begin the 2024 season.[21]
