In 2018, O'Loughlin made his affiliated professional debut for the Low–A Connecticut Tigers, appearing in 7 games and logging a 4.35 ERA with 25 strikeouts in 20+2⁄3 innings of work.[2] He returned to Connecticut in 2019, making 13 appearances (12 starts) and registering a 3.13 ERA with 49 strikeouts across 60+1⁄3 innings pitched.[3]
O'Loughlin did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[4] He returned to action in 2021, splitting the year between the rookie–level Florida Complex League Tigers, Low–A Lakeland Flying Tigers, and High–A West Michigan Whitecaps. On 18 July 2021, while pitching for Lakeland, he was named the Low-A Southeast Pitcher of the Week.[5] In 14 cumulative starts, O'Loughlin worked to a 5–2 record and 2.64 ERA with 52 strikeouts in 61+1⁄3 innings pitched.[6]
He spent the 2022 season back in West Michigan, recording a 4.01 ERA with 50 strikeouts in 51+2⁄3 innings pitched across 27 contests.[7] In 2023, O'Loughlin split the year between West Michigan and the Triple–A Toledo Mud Hens. In 27 games (25 starts), he pitched to a cumulative 6–10 record and 3.99 ERA with 118 strikeouts across 124.0 innings of work. O'Loughlin elected free agency following the season on 6 November 2023.[8]
Oakland Athletics
On November 9, 2023, O'Loughlin signed a minor league contract with the Oakland Athletics organization.[9] In 10 games (8 starts) for the Triple–A Las Vegas Aviators, he compiled a 5.12 ERA with 44 strikeouts across 38+2⁄3 innings pitched. On May 25, 2024, O'Loughlin was selected to the 40-man roster and promoted to the major leagues for the first time.[10] On May 26, O'Loughlin made his major league debut. Entering in relief, he pitched three shutout innings, giving up two hits and a walk while striking out two against the Houston Astros.