By virtue of winning the Supporters' Shield, the Sounders qualified for the CONCACAF Champions League after a two-year drought from the competition.

Source: MLS FC Dallas win 4–2 on penalties after 3-3 aggregate and advance to Western Conference Finals.

For transfers in, dates listed are when Sounders FC officially signed the players to the roster.

For transfers out, dates listed are when Sounders FC officially removed the players from its roster, not when they signed with another club.

Seattle added All-Pac-12 forward Darwin Jones from the Washington Huskies as a Homegrown Player on January 9, 2015.

Only trades involving draft picks and executed after the start of 2015 MLS SuperDraft will be listed in the notes.