Hamm signed with the Seahawks on Thursday, John Boyle of the team's official site reports.
Hamm hasn't played an NFL game since logging five games with the 49ers in 2016, posting two receptions on four targets for 13 yards. He spent last season unemployed, but he'll look to make a comeback with the Seahawks. However, Seattle now has seven tight ends and three of them are locks to make the 53-man roster, so Hamm is considered a long shot.