Sounders FC won their second MLS Cup title at the end of the season,[3] playing in front of a franchise-record 69,274 fans at CenturyLink Field.

[6] Long-time midfielder Osvaldo Alonso, who had served as captain and been with the club since its inaugural MLS season, was released into free agency and signed with Minnesota United FC in January 2019.

[7] Defender Chad Marshall, who had joined in 2014, announced his retirement from professional soccer on May 22, leaving mid-way through the season.

[8] On August 2, defender Román Torres was suspended for ten matches after testing positive for a performance-enhancing substance by the league.

[9] The Sounders clinched a spot in the 2020 CONCACAF Champions League by virtue of having the 4th best record in the regular season and making it to the Western Conference Finals in the Playoffs; the three other teams in the Conference Finals had also clinched berths in the Champions League or were ineligible (in the case of Toronto FC).