The 28 year old, who spend the second half of last season on loan at Goodison Park, joins on a three year deal from Tottenham Hotspur after the Blues thrashed out a late deal for the 21-times capped England international.
Lennon had been rumoured to only want to move back to Merseyside, refusing any and all other offers from clubs in the Premier League, and finally got his move as the summer transfer window shut at 6pm BST.
Toffees manager Roberto Martinez said: “We are delighted to welcome Aaron back to Everton. We know we are getting a player our fans know inside out.
“He had a major role in the second half of our season and we’re looking forward to Aaron kicking on and continuing to enjoy his football, as well as being the productive player we know he can be.
“He is well-respected in the dressing room, his experience in the Premier League is immense and he will immediately add to our squad and to the ambition we have as a club.”
Lennon appeared fourteen times for Everton last season, scoring two goals.