Ryan connected with Jason Snelling and Michael Jenkins in the second quarter to put the Falcons up 17-10 at the half, and then capped a 17-point Falcons third quarter with a 5-yard strike to Roddy White.
Ryan threw for 174 yards as the Falcons (12-2) secured a post-season berth thanks to the New York Giants' loss to Philadelphia earlier Sunday. They also extended their lead in the NFC South to two games after New Orleans was downed by Baltimore.
Michael Turner gained 82 yards on 25 carries for the Falcons, who notched an eighth straight win for the first time since 1998.
Matt Hasselbeck was benched after throwing for 71 yards and two interceptions on 10-of-17 passing for the Seahawks (6-8), who remained atop the NFC West despite losing for the fourth time in five games.