[2] He made his professional debut with the Low–A Aberdeen IronBirds, recording a 1.77 ERA with 21 strikeouts over 14 appearances.
Gillispie did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.
[3] Gillispie returned to Aberdeen in 2021, now a High–A affiliate, and posted a 4–8 record and 4.97 ERA with 78 strikeouts across 21 games (12 starts).
In 27 games (14 starts), he accumulated a 7–4 record and 3.89 ERA with 99 strikeouts and 2 saves across 115+2⁄3 innings pitched.
[6] On December 6, 2023, the Cleveland Guardians selected Gillispie from the Orioles in the minor league phase of the Rule 5 draft.