The all-time top scorer for Manchester United and England shared interim managerial duties with coaches Liam Rosenior, Shay Given, and Justin Walker following Phillip Cocu's sacking earlier in November. However, he's now assumed sole control ahead of Saturday's visit from Wycombe Wanderers.
Rooney has served as player-coach since moving to Derby from D.C. United during the 2019-20 season.
"If I'm not managing the team and I'm part of the coaching staff then I'll continue to play, but if I'm asked to manage the team on a full-time basis then, of course, that will be the end of my playing days, yes," Rooney said Friday, as quoted by Sky Sports News.
"We felt it needed one voice, one person to make the decisions on the team and substitutions during the game and we felt I was the right man for that, so that's where we're at," he added.
"It's exciting for me to do that. Management is always something I've stressed I want to go into, so it's an opportunity for me to try and pick the right team to get a positive result."
The 35-year-old has confirmed he won't be part of Saturday's matchday squad so he can give the contest his "full attention" from the technical area.
Former Middlesbrough and England boss Steve McClaren was drafted in as the Rams' technical director on Tuesday.