[3] He spent his first professional season split between the rookie–level Gulf Coast League Phillies, Low-A Williamsport Crosscutters, and Single-A Lakewood BlueClaws.

In 19 games for Reading, and one start for the High–A Jersey Shore BlueClaws, McArthur posted a 4.25 ERA with 83 strikeouts and 1 save in 78+1⁄3 innings pitched.

[9] On June 29, 2022, McArthur was placed on the 60-day injured list after suffering a stress fracture in his right elbow, and missed the remainder of the season.

[14] He made his major league debut against the Cleveland Guardians on June 28, but surrendered 7 runs on 6 hits and 1 walk in an inning of work; he was optioned back to Omaha the following day.

McArthur began the 2024 season in the major leagues, and recorded his first save on April 5, when he entered in the middle of the 9th inning to replace incumbent closer Will Smith.

[17] He made 57 relief appearances for Kansas City, compiling a 5-7 record and 4.92 ERA with 49 strikeouts and 18 saves across 56+2⁄3 innings pitched.