The 28-year-old winger spent the second half of last season on loan at Goodison Park.
"We are delighted to welcome Aaron back to Everton. We know we are getting a player our fans know inside out," said Toffees boss Roberto Martinez.
"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."