Lynch's agent confirmed the signing Monday night. The 33-year-old running back hasn't played since the 2018 season, when he suited up for the Oakland Raiders.
The five-time NFL Pro Bowler and All-American at the University of California ran for 376 yards and three scores on 90 carries in six starts in 2018, before missing the rest of the season due to a groin injury. Lynch has logged 10,379 yards and 84 rushing touchdowns for his career. The 2012 All-Pro led the NFL with 25 rushing scores from 2013 through 2014, and won Super Bowl XLVIII with Seattle.
Lynch discussed the possibility of returning to Seattle in a video posted to YouTube Monday, though he'd filmed it prior to Seattle's rash of injuries.
"I've been entertaining the idea of maybe going back to go play for Seattle for this playoff run," Lynch said. "That's great and I'm excited for the opportunity. ... At my age, this is a great opportunity to come in, be able to help when needed."
"Get in, do my little thing and then get out," he added. "Hopefully be able to help them go and get the Super Bowl that they should be playing for."
Lynch was drafted by the Buffalo Bills in 2007 and played three and a half seasons before he was traded to Seattle.
The Seahawks (11-4) have a key game ahead with an NFC West matchup against the San Francisco 49ers at 8:20 p.m. EST Sunday in Seattle. The Seahawks can win the division with a victory.