[10] He made his professional debut in 2017 with the Greensboro Grasshoppers of the Single-A South Atlantic League,[11] where he posted a 1–0 record with a 2.93 ERA in four starts[12] before he underwent Tommy John surgery in June, ending his season.

[16] On September 13, 2020, the Marlins selected Garrett's contract and he made his major league debut that day in the second game of a doubleheader.

[17] In two starts in his rookie campaign, he surrendered six runs (five earned) on eight hits and five walks with eight strikeouts in 7+2⁄3 innings.

In 17 turns out of Miami's rotation, Garrett registered a 3-7 record and 3.58 ERA with 90 strikeouts in 88 innings pitched.

[19] Garrett began the 2023 season as a long reliever but joined the Marlins starting rotation in April after Johnny Cueto injured his right biceps.

On January 8, 2025, it was announced that Garrett would miss the entirety of the 2025 season after undergoing a revision surgery on his left ulnar collateral ligament.