Keirsey was drafted by the Minnesota Twins in the 4th round, with the 124th overall selection, of the 2018 Major League Baseball draft.[1] He made his professional debut with the rookie–level Elizabethton Twins. Keirsey split 2019 between Elizabethton and the Single–A Cedar Rapids Kernels, slashing .150/.266/.170 with 14 RBI and three stolen bases across 43 games for the two affiliates.[2] Keirsey did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[3]
Keirsey returned to action in 2021 with Cedar Rapids and the rookie–level Florida Complex League Twins. In 48 total games, he batted .211/.305/.428 with seven home runs, 24 RBI, and 11 stolen bases.[4] Keirsey spent the 2022 campaign with the Double–A Wichita Wind Surge, hitting .271/.329/.395 with seven home runs, 48 RBI, and 42 stolen bases across 121 appearances.[5] In 2023, Keirsey split the year between Wichita and the Triple–A St. Paul Saints. In 130 total games, he slashed .294/.366/.455 with career–highs in home runs (15) and RBI (61), as well as 39 stolen bases.[6]
Keirsey began the 2024 season with St. Paul, batting .292/.363/.477 with 14 home runs, 75 RBI, and 36 stolen bases over 103 games.[7] On September 5, 2024, Keirsey was selected to the 40-man roster and promoted to the major leagues for the first time.[8]