Garrett had his contract selected by the Marlins on Sunday and will serve as the 29th man for the doubleheader against the Phillies.
The 23-year-old could make his major-league debut during Sunday's twin bill, though he'll likely be headed to the alternate training site after the second game. Garrett spent most of 2019 at High-A Jupiter and had a 3.34 ERA, 1.23 WHIP and 118:37 K:BB over 105 innings.