The former England captain is expected to sign a three-and-a-half year contract with DC United.
Rooney, 32, is the all-time leading goal-scorer for both Manchester United and the English national team.
Rooney, who turns 33 in October, will occupy a designated player spot on the club's roster and he will be officially added to the squad when the transfer window reopens on 10 July, pending receipt of worldwide clearance.
Rooney signed a 3½-year contract, according to the club, and can be added to the roster officially on July 10, when the global transfer window opens.
Wayne Rooney will be confirmed as a DC United player on Thursday, Sky sources understand.
Wayne Rooney scored 11 goals in 40 matches last season in his second stint with boyhood club Everton.
'Moving to America and MLS fulfils another career ambition for me.
The legendary English forward, with a few years of top end football left in him, was considering his player option, but also sent delegates to the United States in May to discuss a potential move to the MLS. He's expected to make his debut for the club at Audi Field on July 14, when they play the Vancouver Whitecaps. I have the hunger to be a success here and will give DC 100% - as I have always done for every team I have ever played for.
The club's general manager David Kasper said of the move: "Wayne is undoubtedly one of the best players in Premier League history and his goal scoring record for club and country speaks for itself".
"This is a seminal moment for our fans and organization. We are beyond excited to add someone of Rooney's caliber and we are thrilled to welcome him to D.C".