The striker scored a penalty to give United a 1-1 draw at Blackburn Rovers, which clinched the title for the Old Trafford club.
It is United's 19th league championship, surpassing Liverpool as the country's most successful team.
Rooney chose a novel way to celebrate, taking a razor to his chest and posting the result on his Twitter account accompanied by the comment 'Champions'.
Team-mate Michael Owen then Tweeted: "None of us thought Wazza would send that picture! He is madder than we thought!!!"
- Manchester United
- Blackburn Rovers
- Premier League
- Wayne Rooney