Barnes agreed to a minor-league contract with the Mariners on Wednesday, Tacoma Rainers broadcaster Mike Curto reports.
Barnes was cut loose by Detroit over the weekend after posting a 6.10 ERA, 1.45 WHIP and 10:9 K:BB across 20.2 innings this season. He'll report to Triple-A Tacoma in hopes of earning another big-league opportunity with the Mariners.