The 2009 season was Seattle Sounders FC's debut in Major League Soccer. The inaugural game was on March 19, 2009 at Qwest Field in Seattle, Washington against the New York Red Bulls. Sounders FC beat the Red Bulls 3–0 in front of a sell-out crowd.

On August 5, 2009, Sounders FC set a stadium and Washington record for most people watching a soccer game against FC Barcelona with an attendance of 66,848.

In a press conference on November 13, 2007, MLS announced the award of an MLS expansion team franchise to Seattle. In 2008, Sounders FC developed the Starfire Sports Complex in Tukwila and the USL team played most of the 2008 season at the updated facility. At the time, the USL team's management thought that practicing and playing at Starfire could provide more continuity and a smoother transition for those hoping to play for the new MLS franchise.

In early December 2008, Seattle Sounders FC reportedly offered a coaching contract to Sigi Schmid, who led the Los Angeles Galaxy to a MLS Cup in 2002 and the Columbus Crew to a MLS Cup in 2008. However, before Schmid could respond to the contract offer, the ownership of the Columbus Crew filed a tampering complaint with the MLS that put the offer on hold. The Crew's ownership complained that Schmid had communicated with Sounders FC during the 2008 season, despite being denied permission to do so, and that he shared confidential information with Sounders FC after leaving the Crew. The MLS ruled that no tampering occurred, but ordered Sounders FC to financially compensate the Crew before signing Schmid. Sounders FC officially introduced Schmid as their first coach on December 16. Former USL Sounders player and head coach Brian Schmetzer was retained as the top assistant coach, and Tom Dutra was selected as goalkeeper coach. Retired Major League Soccer veteran defender Ezra Hendrickson joined the Sounders as an assistant coach in January, 2009. Former MLS player and Everett, Washington, native Chris Henderson was named technical director on January 24, 2008. Joining Henderson in the front office is longtime Seattle Seahawks VP Gary Wright as the senior vice president of business operations. Drew Carey was named the chairman of the Membership Association.

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