The experienced centre-back has now made 259 appearances for the Toffees since arriving from Burnley in July 2017, with 223 of those outings coming in the Premier League.
Keane has also scored 19 goals during his Everton career and earned nine of his 12 England caps while representing the Merseyside club.
The 33-year-old has played a significant role this season as Everton continue to show progress under David Moyes, making 30 appearances in all competitions and helping the side register 11 Premier League clean sheets.
Speaking after signing his new deal, Keane told evertontv: “I’m really happy.
“The club means a lot. It’s one of those things that’s easy to say, but it has become part of me.
“It’s who I am and it feels like family to me – the people around the club, the fans, the players, the staff.
“So it’s really special to me and I couldn’t really imagine my life without Everton.”
Keane admitted there was uncertainty surrounding his future last summer, but says this campaign has been one of his most satisfying personally.
He added: “I think it’s been a great season for me personally.
“I’ve played a lot of football – probably more than I expected – and I feel like I’ve done well and I’ve absolutely loved it.
“To get my 10th year here, I think it’s a big achievement and one I’m proud of.”
The defender also praised Moyes for helping restore confidence and consistency to his game.
Keane said: “I think the manager’s been amazing for me.
“He’s put a lot of faith in me and given me that trust, and I like to think I’ve repaid that.”
Everton head into the final weeks of the season in a far healthier position than in previous years, and Keane says there is renewed optimism around the club.
With his future now secured, the veteran defender will hope to remain a key figure as Everton continue building under Moyes.