Garton was traded to the Mariners along with minor-league catcher Mike Marjama for minor-league pitcher Anthony Misiewicz, minor-league infielder Luis Rengifo and a player to be named later.
The 27-year-old Garton will assume a spot on the Mariners' 40-man roster, taking the spot of Tuffy Gosewisch, who was designated for assignment in a corresponding move. Garton had previously yielded 10 runs in seven relief appearances with the Rays earlier this season but had been dominant at Triple-A Durham, recording a 1.64 ERA and 46 strikeouts over 33 innings. He'll head to the Pacific Coast League with his new organization, reporting to Triple-A Tacoma.