The Seattle Mariners selected Plassmeyer in the fourth round, with the 118th overall selection, of the 2018 Major League Baseball draft.[3] He signed and was assigned to the Low–A Everett AquaSox, going 0–1 with a 2.25 ERA and 44 strikeouts in 24 innings pitched.[4] He was a 2018 NWL mid-season All Star.[5]
Tampa Bay Rays
On November 8, 2018, the Mariners traded Plassmeyer, Mike Zunino, and Guillermo Heredia to the Tampa Bay Rays in exchange for Mallex Smith and Jake Fraley.[6] He began the 2019 season with the Single–A Bowling Green Hot Rods, for whom he was 2–1 with a 1.23 ERA.[7] He was a 2019 MiLB organization All Star, and finished the year making appearances for the High–A Charlotte Stone Crabs and Triple–A Durham Bulls. In 25 total games (23 starts), he accumulated a 9–3 record and 1.91 ERA with 109 strikeouts in 132 innings of work.[5] Plassmeyer did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[8] He returned to action in 2021 for the Double–A Montgomery Biscuits, for whom he logged a 3.64 ERA across 7 contests.
The Phillies selected Plassmeyer's contract on August 22, 2022, and he was called up to the majors.[12] On August 23 he made his debut, pitching 1+1⁄3 perfect innings, striking out Austin Romine on three pitches with the bases loaded.[13]
Plassmeyer was optioned to Triple-A Lehigh Valley to begin the 2023 season.[14] In 11 games (10 starts), he struggled to a 6.95 ERA with 47 strikeouts in 44 innings of work. On June 20, 2023, Plassmeyer was released by the Phillies.[15] Plassmeyer re–signed with the Phillies on a minor league contract on June 23.[16] On September 30, the Phillies selected Plassmeyer's contract, adding him back to the major league roster.[17] That day he made his first MLB start against the New York Mets, surrendering 10 runs (9 earned) on 8 hits with 4 strikeouts across 3+2⁄3 innings pitched.[18] Following the season on November 6, Plassmeyer was removed from the 40–man roster and sent outright to Triple–A Lehigh Valley.[19] He elected free agency the same day.[20]
Pittsburgh Pirates
On January 4, 2024, Plassmeyer signed a minor league contract with the Pittsburgh Pirates.[21] In 28 games (11 starts) for the Triple–A Indianapolis Indians, he struggled to a 5–10 record and 7.93 ERA with 70+1⁄3 innings pitched. Plassmeyer elected free agency following the season on November 4.[22]
Texas Rangers
On December 10, 2024, Plassmeyer signed a minor league contract with the Texas Rangers.[23] He made 28 appearances (16 starts) for the Triple-A Round Rock Express in 2025, registering a 9-4 record and 4.43 ERA with 99 strikeouts across 105+2⁄3 innings pitched. Plassmeyer elected free agency following the season on November 6, 2025.[24]
Toronto Blue Jays
On December 6, 2025, Plassmeyer signed a minor league contract with the Toronto Blue Jays.[25]
Personal life
Plassmeyer's father, Marty, and older brother, Mitch, both played college baseball as left-handed pitchers. Marty played for Nicholls State University and Mitch played for Bradley University.[26] Mitch is currently the bullpen coach for the Baltimore Orioles.
