Rooney had previously played for United in 2018 and 2019 before leaving the franchise to join Derby County as a player coach in the Championship.
The 36 year-old kept Derby up after taking over from Phillip Cocu as permanent manager in January 2021 but relegation still loomed, remarkably finishing seven points from safety after a 21-point deduction at the start of last season.
Rooney believes coming back to the MLS to coach is not a backward step, but moreover, that his time at Derby County prepared him for this role.
"I've seen a few articles, certainly back in England, on this being a possible backward step in my managerial career," he said.
"I really find that a bit disrespectful to this league. I feel the experience I've gained at Derby County over the past 18 months has been great for my development as a coach, as a manager.
"To come here back to the MLS, back to D.C. United, was an exciting challenge for me - something which I feel can develop me as a coach."
United faces an uphill battle to make the MLS playoffs, sitting nine points from seventh-placed FC Cincinnati in the Eastern Conference, despite two games in hand.
The four-time MLS Cup winners have been without a head coach since April and interim Chad Ashton's tenure reached a nadir last weekend, following a 7-0 defeat to Philadelphia Union.
Ashton will remain in charge until Rooney receives his work visa, but Rooney believes he is more than suited for the task at hand.
"The team need to improve, I think that's obvious for everyone to see," he said. "I really think with my capabilities of developing young players - of course we're working hard to get a few new players in - we can really get this club to successful ways again.
"I'm an ambitious person. One day I want to manage at the top level, and this is part of that process in terms of coming here and trying to develop this club, trying to get success here, but also develop myself as a manager."