The team were managed by Sigi Schmid until his firing in late July; he was replaced by Brian Schmetzer on an interim basis.

The Sounders won their first MLS Cup in the 2016 final against Toronto FC, which ended in a penalty shootout after a scoreless draw.

Note: Flags indicate national team as defined under FIFA eligibility rules.

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

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