The 34-year-old was forced to retire due to a knee injury that has kept him sidelined since May 4.
Marshall ends his career as one of the greatest defenders to ever play in MLS, having become the only player in league history to win MLS Defender of the Year three times (2008, 2009, 2014).
“After more than 15 years of living my childhood dream, the time has come for me to hang up the boots,” Marshall said in a team release.
“I’d like to thank everyone that has played a part in my career. To my teammates, support staff and coaches: you’ve been my second family. The locker room is what I’ll miss the most. Thank you to the fans of Seattle and Columbus for supporting me throughout the years, as well as the Sounders FC and Columbus Crew SC organizations for giving me a chance to represent them on the field.
"Most importantly, I’d like to thank my family. I’m forever indebted to them for the sacrifices they’ve made in allowing me to pursue this dream. From heartbreaking losses to MLS Cup wins, own goals to cartwheels, it’s been a blast.”
Marshall spent 10 years with the Columbus Crew after being selected in the 2004 MLS SuperDraft, before he was traded to Seattle in 2014.
“Thank you, Chad. It was a privilege to have such a smart, humble player as part of the Sounders for so long, one of the greatest careers for any domestic player in MLS history,” said Sounders general manager Garth Lagerwey.
Overall, Marshall won seven major trophies during his career: two MLS Cups (2008 with Columbus; 2016 with Seattle), four Supporters’ Shields (2004, 2008 and 2009 with Columbus; 2014 with Seattle), and the 2014 U.S. Open Cup with Seattle.
Marshall ranks second all time among field players in career MLS appearances, starts and minutes played.
Internationally, Marshall earned 12 caps for the U.S. men's national team in his career, scoring one goal.
“Ever since he came to Seattle, Chad has been a massive influence on our franchise, whether it was his play on the field or his impact off of it, he is a true champion,” said Sounders head coach Brian Schmetzer.
“It’s hard to put into words all of the positive things he has brought to the club and his teammates. It has been an honor to coach such a fantastic American player, arguably one the best defenders in MLS history. I’d like to thank him for what he’s done in the Sounders community and wish him the best in whatever he decides to do next. We, the players and staff will miss him, and our league has lost a great player.”