Simpson was recalled Tuesday from Triple-A Jacksonville, Jordan McPherson of the Miami Herald reports.
Simpson has struck out 62 batters in 36.1 innings this season in the minors, but all of those punchouts have come alongside a 4.71 ERA and 1.54 WHIP. The 26-year-old left-hander will be making his major-league debut whenever he gets into a game for the Marlins.