Despite having more than two years remaining on his contract in America, Rooney has expressed a desire to return to England after just over a year and will join last season’s Championship play-off beaten finalists on an initial 18-month contract with the option for a further year.
Rooney, who has previously expressed a desire to move into management, will work primarily with Derby’s academy.
Rooney will stay with DC United until the conclusion of the ongoing MLS season in November before joining the Rams at the turn of next year.
"I am very excited about the opportunity that Derby County have provided me with,” Rooney told Derby’s official website.
"I am looking forward to joining Phillip Cocu, his coaching staff and the first-team squad from the start of January. I am sure I can make a big contribution and can’t wait to meet everyone, especially the supporters.
"I am equally excited to begin my coaching career at Derby County working with both the first team and Academy.
"I must also take this opportunity to thank DC United, their owners, executives and supporters who have been superb to work with. I want them to know that I will give my all in support of our push for the play-offs."
Rooney moved to DC United from Everton last year and his arrival represented a major upturn in fortune for the side as his 12 league goals catapulted them from the bottom of the Eastern Conference to seal a playoff spot.
The 33-year-old former Manchester United and Everton striker played for 16 seasons in the English top flight from 2002 to 2018, scoring 208 goals in 491 Premier League appearances before joining DC United in June 2018.
