Team president Dave Dombrowski confirmed the agreement Friday. Hanrahan, a former All-Star, has battled elbow problems of late. The right-hander had Tommy John surgery in May 2013 and hasn't pitched in the majors since.
Dombrowski says Hanrahan will start throwing after Thanksgiving.
The Tigers acquired Hanrahan about a month into this season, but he never made it to their big league roster. Dombrowski says he thinks Hanrahan could have gone for a guaranteed deal elsewhere, but the reliever basically felt he owed the Tigers after being unable to contribute last season.