Minor leagues Lynch was selected by the
Kansas City Royals with the 34th overall pick in the
2018 Major League Baseball draft. He signed with the Royals on June 10, 2018, for $1.7 million. He made his professional debut with the
Burlington Royals of the
Rookie-level Appalachian League before being promoted to the
Lexington Legends of the
Single–A South Atlantic League. In 12 starts between the two clubs, he went 5–1 with a 1.58 ERA and a 1.01 WHIP. Lynch spent 2019 with the
Wilmington Blue Rocks of the
High–A Carolina League and was named a Carolina League All-Star midway through the season. Over 15 starts, he went 5–2 with a 3.10 ERA. He was selected to play in the
Arizona Fall League for the
Surprise Saguaros following the season, earning All-Star honors. He did not play any minor league games in 2020 due to the cancellation of the minor league season because of the
COVID-19 pandemic.
Major leagues On May 2, 2021, the Royals announced that Lynch would be promoted for the next day's game and be the starting pitcher against the
Cleveland Indians. Lynch was officially added to the
40-man roster on May 3, and given the number 52. In 2022, Lynch made 27 starts for Kansas City, registering a 4–13 record and 5.13 ERA with 122 strikeouts in innings pitched. After missing the first two months of the 2023 season with a left shoulder strain, Lynch was placed back on the injured list with the same ailment on July 19, 2023. In his time on the active roster in between IL stint, he had recorded a 4.64 ERA with 34 strikeouts in innings across 9 starts. Lynch was transferred to the 60–day injured list on September 6. Optioned to the Triple–A
Omaha Storm Chasers to begin the 2024 season, Lynch was quickly recalled to join the starting rotation in May . Lynch settled into a left-handed relief role becoming a staple of the Royals bullpen with occasional starts as an "opener" for bullpen games. In 2025, Lynch set career highs in WAR (1.3), ERA (3.06), ERA+ (135) and appearances (57). ==Personal life==