Rooney, 31, is back at his boyhood club 13 years after leaving for Old Trafford, where he won five Premier League titles and the Champions League.
It will be an emotional return to Merseyside for Rooney – 13 years after moving down the M62 for £25.6million.
Rooney has signed a two-year deal with the Toffees, and will be looking to win his place back in the England team having secured his move.
“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,” said Everton manager Ronald Koeman.
“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 was given a warm reception by Everton fans when he left the Finch Farm training complex following his medical on Saturday.
United manager Jose Mourinho insists that Rooney has been a “model professional” throughout his time at Old Trafford.
Mourinho said: “It is no secret that I have long been an admirer of Wayne; he has been a model professional throughout his time at the club and will remain in the history books for many years to come.
“It is never easy to see a great player playing less football than he would like and I could not stand in his way when he asked to go back to Everton. His experience, focus and determination will be missed and I wish him well for the future.”
United’s executive vice chairman Ed Woodward added: “Wayne has been a fantastic servant to United since the moment he signed for us as a prodigiously talented, explosive teenager some 13 seasons ago.
“Wayne leaves us as our greatest ever goalscorer and having won every major trophy in the game.
“His record will take decades for anyone to get close to matching and I am extremely grateful for the way he has led from the front since being appointed club captain three years ago.”
The deal has been confirmed after Romelu Lukaku’s £75million move in the other direction was confirmed.
Rooney is understood to be prepared to take a significant cut on his £250,000-a-week basic salary at United in order to return to Everton.
He met with Toffees boss Ronald Koeman, who warned the player he will not tolerate any bad behaviour.
Koeman outlined his football vision including his tough disciplinary code for all of his players.