The Marlins recalled McMillon from Triple-A Jacksonville on Friday.
McMillon was claimed off waivers from the Royals a week ago and will now receive an opportunity in the big-league bullpen. The right-hander made four appearances with Kansas City last season, allowing one run. He's posted a 6.32 ERA and 37:27 K:BB over 31.1 innings at the Triple-A level in 2024.