The Mariners announced the deal on Tuesday. Instead of waiting to see if Furbush would become eligible for arbitration, the sides reached a one-year deal.
Furbush, 27, appeared in a team-best 71 games last season. He was 2-6 with a 3.74 ERA and a .199 opponent batting average. The left-hander tied for 10th in the American League in appearances and 13th with 20 holds.
Furbush has spent parts of three seasons with Seattle. He was acquired in a trade with Detroit in July 2011.