Rooney recently stepped down from a tumultuous 18-month spell in charge of Derby County which ultimately culminated into relegation to the League One at the end of the 2021/2022 season.
The former England and Manchester United captain played for DC United at the twilight of his career, making 52 appearances and scoring 25 goals.
Rooney has now been tasked with reviving DC's fortunes in the MLS, with the club second from bottom in the Eastern Conference following a crushing 7-0 defeat to Philadelphia Union last week.
At his unveiling as DC's new boss, Rooney denied assertions that a move to the MLS represented a step back in his managerial career.
"I've seen a few articles back in England about this possibly being a backwards step in my managerial career," Rooney said. "I really find that a bit disrespectful to this league.
"I feel the experience I gained at Derby County over the past 18 months has been great for my development as a coach, as a manager. And to come here, back to the MLS, back to DC United was an exciting challenge for me, something that can develop me as a coach but also [help] the team to improve.
"I really believe with my capability of developing players, young players - and of course we're working hard to get a few new players in - we can really get this club back to successful ways again. It's going to take a lot of hard work but that's what I'm here to do and really improve the team."
Jason Levien and Steve Kaplan, co-chairmen of D.C. United, said in a statement: "Wayne is a soccer legend and one of the most exciting and dynamic up-and-coming managers in our sport. He's already proven in his young coaching career that he knows how to lead a group through adversity.
"He has an understanding of our league and what it takes to be successful in Major League Soccer thanks to his two-year stay with us as a player. The passion he showed while wearing Black-and-Red electrified our city and our club and we are so excited to welcome him back as our head coach."
