It is Rooney’s second job in management after he left Derby County last month and he rejected criticism at his return to the American club.
“I’ve seen a few articles, certainly back in England, on this being a possible backward step in my managerial career,” said the 36-year-old.
“I really find that a bit disrespectful to this league.”
Rooney said he had spoken to his wife first after DC United came in for him and events leading to him taking up the role progressed quickly.
“Any major decisions I make like this are discussed with my wife,” he said. “My family will, for the time being, stay in England and come over and visit.
“There were a few other clubs – both in England and in Europe – who got in touch. My plan really was to, after Derby County, take a bit of a break and then see what comes up.
“Once my agent called and said DC had come in, it was quite quick really – probably within 24 hours.”
England and Manchester United’s record goalscorer spent 18 months at DC United and captained the side before joining Derby as a player-coach in January 2020.
Rooney went on to manage the club through a period when they were in administration and was in charge as they were relegated to League One last season.
“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,” added Rooney.
“To come here back to the MLS, back to DC United, was an exciting challenge for me – something which I feel can develop me as a coach.
“The team need to improve, I think that’s obvious for everyone to see, and 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.
“It’s going to take a lot of hard work, but that’s what I’m here to do and really improve the team.”
DC United said Rooney is “one of the most exciting and dynamic up-and-coming managers in our sport”.
Co-chairmen Jason Levien and Steve Kaplan added in a statement: “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.”
DC United have been without a manager since April, are second bottom of the Eastern Conference and were beaten 7-0 by Philadelphia Union on Friday.
Interim head coach Chad Ashton will remain in charge of the team until Rooney has received his work visa.
“I’m an ambitious person,” added Rooney.
“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.”
Rooney was put in interim charge of Derby in November 2020 with the club bottom of the Championship after they parted company with Phillip Cocu.
He was confirmed in the post on a two-and-half-year contract three months later, a decision which prompted him to confirm his retirement as a player.
Derby entered administration in September 2021 and last season were relegated from the Championship, having been docked 21 points throughout the season.
The finished seven points from safety and, if the points deduction had not been imposed, they would have stayed up in 17th place.
The former Everton forward, who made his professional debut for the Toffees in August 2002 aged just 16, then quit Derby on 24 June.
“Wayne is a winner and a competitor. His work ethic and what he demands of himself and his players is second to none,” said Dave Kasper, DC United president of soccer operations.
“Wayne’s approach to the game and the style of soccer he wants to play fits within our philosophy and we believe he is the right person to lead our club moving forward.”