The 31-year-old forward returns to his boyhood club, 13 years after he left Goodison Park, on a two-year deal.
During his time at Old Trafford, Rooney scored 183 Premier League goals.
His 253 goals overall make him United’s all-time leading goalscorer.
Back at Everton, he will look to become only the second player to score 200 Premier League goals, after Alan Shearer.
Rooney is two goals away from this landmark.
Everton, for whom Rooney is the sixth senior signing of the summer, open the season at home to Stoke City on 12 August.