Quinn's deal was finalized on Thursday, but terms of the contract were not available. Quinn and the Seahawks agreed to terms of the contract earlier this week.
Quinn joins Josh Portis as the expected backups to Wilson. Quinn played last year for the Chiefs, starting eight games. It was his first regular-season playing time since the 2009 season.
Backup safety Chris Maragos also signed his one-year contract tender on Thursday. Maragos was a restricted free agent and a special teams standout for the Seahawks last season.