Seattle also agreed to terms on one-year deals with cornerback Roy Lewis and guard Deuce Lutui.
Ruud adds a veteran presence to the Seahawks' young linebacker corps and replaces David Hawthorne, who signed with New Orleans on Tuesday.
Ruud, Nebraska's career tackles leader, played nine games for the Tennessee Titans last season before being placed on injured reserve with a groin injury. Ruud had 57 tackles and one interception for Tennessee. He played his first six NFL seasons with the Tampa Bay Buccaneers.
Lutui played for Seattle head coach Pete Carroll at USC before spending the last six seasons with the Arizona Cardinals. Lutui could potentially challenge for the starting job at left guard after the release of Robert Gallery last month.
Lewis has played the last three seasons in Seattle, primarily as a nickel back and special teams standout. He was the special teams captain in 2010 before a knee injury landed him on injured reserve. The injury lingered into last season as he landed on the physically unable to perform list for the first six games. Lewis appeared in 10 games for Seattle and recorded 20 tackles last season.