The Seahawks confirmed the agreement Thursday. Jackson is a favorite in the Seahawks locker room and a capable backup to Russell Wilson.
Jackson was part of the three-way quarterback competition that Wilson won during the 2012 preseason. He was later traded to Buffalo but never got into the mix with the Bills.
He was released last preseason and immediately brought back to Seattle to serve as Wilson's backup. Jackson appeared in three games during the 2013 regular season and even got a few snaps in Seattle's Super Bowl win over Denver.
Jackson started 14 games for Seattle in 2011 while playing through a chest injury.