A distinguished career in the Premier League saw Rooney become Manchester United's all-time record goalscorer between two spells with Everton, while he is also England's top marksman in global football.
The 32-yearold will complete the formalities of his move when the MLS transfer window opens on July 10.
There is no transfer fee but it is understood DC United have agreed a compensation package with the Toffees.
He signed a 3½ year designated-player contract with D.C. United and is expected to make his debut July 14 when the team opens its new stadium in Southeast Washington against the Vancouver Whitecaps.
According to The Washington Post, Rooney is signed on a guaranteed deal worth almost $13 million, making him the highest-paid player in club history.
'When I visited earlier this summer I was really impressed with everyone I met connected with the club, and of course the new Audi Field. He scored 208 goals in the Premier League, second only to Alan Shearer's 260.
Rooney's 53 goals and 119 games lead England in worldwide play.
"Now I can't wait to get on the pitch in a United shirt and join my new team-mates to bring success to this club".
"He is a world-class player and he elevates those around him, both through his work ethic and winning mentality", general manager Dave Kasper said.
Now his attention will turn to life at DC United and ensuring he enjoys a successful end to his career. "Wayne has thrived when competing at the most elite levels of soccer and we're thrilled to have his leadership as we enter this new era at Audi Field". "I also think it is obviously great for the league, but I think for Wayne personally", Beckham told MLS.