Last week, the winless Bills released quarterback Trent Edwards.
The team is in a rebuilding mode under first-year general manager Buddy Nix and coach Chan Gailey and had depth at the position with Fred Jackson and rookie first-round draft pick C.J. Spiller.
The Seahawks (2-2) are looking to beef up their running game under first-year coach Pete Carroll. Justin Forsett leads Seattle with 215 yards and no touchdowns. Julius Jones has 12 carries for 30 yards.
After losing his starting job to Jackson last season, Lynch reclaimed the job in Week 2 this year and led the Bills with 37 carries for 164 yards. In 45 career games, he has 2,765 yards rushing and 17 touchdowns, along with 670 yards receiving and a score.
The deal comes two weeks before the NFL trade deadline, and marks a turnaround in philosophy for the Bills, who said last spring they had no intention of trading him. Lynch had been seeking a fresh start after his reputation in Buffalo took a hit following his off-field troubles.
In June 2008, he pleaded guilty to a traffic violation and admitted to driving off after striking a female pedestrian with his car near Buffalo’s downtown bar district.
AP Sports Writer Tim Booth in Seattle contributed this story.