Garton cleared waivers and was outrighted to Triple-A Tacoma on Thursday.
Garton will stay in the organization after being ousted from the 40-man roster earlier in the week. The 27-year-old owns an unremarkable 4.55 ERA in 61.1 major-league innings over his career, though he posted a 1.54 ERA and 0.51 WHIP in 11.2 innings for the Mariners after being acquired via trade in August. He'll fight for a spot in Seattle's bullpen to start 2018, though he may wind up as pitching depth at Tacoma to start the year.