Rooney re-joined Everton from Manchester United in last summer's transfer window, and England's record goalscorer scored 10 Premier League goals for the Toffees last term.
Speculation linking the player with a move to the MLS has gathered pace over the last month, however, and Everton have now announced that the forward will leave Goodison Park to join DC United.
"Rooney will complete the formalities of his move when the MLS transfer window opens on July 10," read a statement on Everton's official website.
"From everyone at Everton, we thank Wayne for his service to the club and wish him every success in the next three-and-a-half years with DC United."
The 32-year-old has scored 208 Premier League goals for Everton and United, and he won five Premier League titles, one FA Cup and one Champions League during his time at Old Trafford.
Rooney is expected to arrive in Washington on Thursday night, and will reportedly speak to the media for the first time as a DC United player at the start of next week.