Marshall was traded to Seattle Sounders FC on 10 February 2009 for allocation money. He scored his first goal for the Sounders against Chicago Fire as the game finished 1–1. He also assisted a goal by Steve Zakuani in a match against San Jose. However, in the 86th minute in a match against D.C. United, Marshall accidentally scored an own goal with his head, and the game finished 3–3. He scored his second goal for the club on 17 October, in a game against Kansas City Wizards.