The trade was announced on Thursday morning.
Marshall has spent the past 10 seasons with Columbus and was a two-time MLS defender of the year in 2008 and 2009. He also earned MLS Best XI honors those seasons. He ranks 21s among active players with 253 MLS appearances and has 11 caps for the U.S. national team.
It's the third trade Seattle has made in three days, having acquired goalkeeper Stefan Frei from Toronto and sending midfielder Mauro Rosales to Chivas USA for forward Tristan Bowen earlier this week.