The Everton striker is signing a three-and-a-half-year contract worth £12.5million.
The Daily Mail says it is understood there is no transfer fee attached to the move but an agreement has been reached over the remaining year of Rooney's £140,000-per-week Everton contract.
"It is fantastic to be joining DC United at such an exciting time in the club's history with the new stadium opening in just a few weeks," Rooney said.
"Moving to America and MLS fulfils another career ambition for me. I have the hunger to be a success here and will give DC 100 per cent - as I have always done for every team I have ever played for.
"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. Now I can't wait to get on the pitch in a United shirt and join my new teammates to bring success to this club."
"I think it's the right move for him. I think he'll do really well. I think DC is the right club for him. I think it's a great city for him to move with his family and enjoy the time that he's going to be there."