The 24-year old joined the Toffees from Burnley for a fee worth an initial £25m that could rise to £30m.
Keane resisted the lure of signing for his boyhood club, Manchester United, to make the move to Merseyside.
"I'm absolutely delighted to be at Everton, a fantastic football club with passionate fans and a great tradition and I can't wait to come into training tomorrow to meet all the lads," Keane told the club's website.
| We've signed Michael Keane on a five-year deal for a fee which could rise to a Club-record £30m
— Everton (@Everton) July 3, 2017