“Wayne has shown me that ambition that we need and that winning mentality – he knows how to win titles and I’m really happy he’s decided to come home,” manager Ronald Koeman told the club’s official website.
“He loves Everton and he was desperate to come back. He is still only 31 and I don’t have any doubts about his qualities. It’s fantastic he’s here.”
Rooney rejoins his boyhood club after a 13-year stay at Old Trafford, during which time he became Manchester United’s all-time leading goalscorer with 253 goals in 559 appearances.
The 31-year-old striker, who is also England’s leading goalscorer of all time, burst onto the scene as a 16-year-old with Everton in 2002, making 77 appearances and scoring 17 goals for the club before leaving for United in 2004.
He leaves United having won every honour available to him in the English game, including five Premier League titles, the FA Cup, three League Cups, the Champions League and the Europa League.
The 119-time capped England international is also a former PFA Player of the Year, FWA Footballer of the Year and Premier League Player of the Season.