Hart, who missed nearly two months with a left hamstring injury, will be available for Friday’s game against the Chicago White Sox. A two-time All-Star in the National League, Hart was batting .209 with five home runs and 17 RBI in 37 games before suffering the injury against Minnesota in May.
Seattle designated outfielder Cole Gillespie for assignment to make room for Hart on the roster. Hart, 32, missed the entire 2013 season after undergoing multiple knee surgeries last year. He hit .297 with one home run and four RBI in 10 rehab starts with Triple-A Tacoma.
The Mariners trail the Athletics by five games in the American League West and hold the second wild card spot.
-- Chris Johnson