Keane joined the Toffees from Burnley in the summer of 2017 for £25m and has made 94 Premier League appearances in his time on Merseyside.
The 27-year-old was one of Carlo Ancelotti’s best players last season, as he made 31 appearances in the top flight to help Everton steer clear of the relegation places and cement a place in mid-table.
Keane’s impressive form has seen him earn a recall to England manager Gareth Southgate’s squad for Nations League matches against Iceland and Denmark next month.
"I have loved my three years at Everton and am looking forward to seeing what the future holds," Keane told Evertontv.
"I am learning every day on the training pitch with the manager and all his staff. They have been brilliant and really got across the way they want us to play. The manager is one of the best there has been.
"I am hoping we can kick on this season and make the fans proud again. Before lockdown I had a good run of form and, hopefully, I can keep that going into this season and keep improving.
"I am not happy just staying where I am at the minute. I want to keep improving and keep learning. My best years are definitely ahead of me.
"I am working on things every day… striving to get better in every part of my game and, hopefully, I can show that."
Everton will begin the 2020/2021 campaign with a trip to Tottenham on September 13 after the international break.
