The Toffees' official Twitter account noted the deal was done, with the England captain signing on for two years with his boyhood club:
"It's a great feeling to be back," Rooney said, per the club's official website. "I'm excited; I cannot wait to meet the lads, get on the training pitch and then get on the pitch to play. "I'm ecstatic—I just cannot wait to get back playing."
The transfer brings an end to 13 distinguished years at Old Trafford. Rooney won five Premier League titles with the Red Devils, as well as the UEFA Champions League in 2007-08 and the FA Cup in 2015-16.
The forward also departs as the leading goalscorer in United's history, with 253, a record Sir Bobby Charlton previously held.
Following the announcement, Manchester United provided a statement from manager Jose Mourinho:
"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."
Despite his longstanding association with the Manchester outfit, the time is right for Rooney to pursue a new challenge.
After all, following a difficult start to the 2016-17 season under the recently installed Mourinho, the England captain was relegated to the bench. Rooney's form was poor early in the campaign, as he failed to make an impression at the point of the attack, as a support striker, from out wide or even in midfield.
Given he's approaching the twilight of his career at 31, it's no surprise he has opted to leave.
Everton boss Ronald Koeman will be hoping the switch back to Goodison Park can rekindle something in Rooney. When he's at his best, there's a fire in his belly—although it's not something we've seen frequently in recent seasons.
The Blue Room's Ell Bretland is excited to see what Rooney has to offer in his second spell with the club:
It would be unfair to accuse Rooney of settling into a comfort zone at Old Trafford, as his honours list paints him as a serial winner. But the chance to play in his beloved royal blue again will surely stir something in him, even given the amount of football he's played in his career.
His final couple of seasons at United may have blemished Rooney's Red Devils legacy slightly, but to have been such a key member of the team for so long is credit to both his talent and durability.
It will be a long time before another player betters Rooney's longevity and success at what is one of the world's most demanding clubs.