John Mitchell McMillon (born January 27, 1998) is an American professional baseball pitcher for the Kansas City Royals of Major League Baseball (MLB).

McMillon attended Jasper High School in Jasper, Texas. He was drafted by the Tampa Bay Rays in the 21st round of the 2016 Major League Baseball draft. He did not sign with the Tigers and played college baseball at Texas Tech University. In 2018, he played collegiate summer baseball with the Chatham Anglers of the Cape Cod Baseball League.^[1] After his junior season, he was drafted by the Detroit Tigers in the 11th round of the 2019 MLB draft, but again did not sign and returned to Texas Tech for his senior season.^[2]

After going undrafted in the 2020 MLB draft, McMillon signed with the Kansas City Royals.^[3] He was assigned to Single–A Columbia to begin the season, later being promoted to the High–A Quad Cities River Bandits. After posting a 2.70 ERA in 13 games, he was again promoted to the Double–A Northwest Arkansas Naturals, where he logged a stellar 0.87 ERA with 30 strikeouts and 5 saves in 20+2⁄3 innings pitched.^[4]

On August 16, 2023, McMillon was selected to the 40-man roster and promoted to the major leagues for the first time.^[5] On August 30, the Royals placed McMillon on the 15-day injured list with a strained right forearm, retroactive to August 28.^[6]

McMillon was optioned to the Triple–A Omaha Storm Chasers to begin the 2024 season.^[7]