New Everton boss Frank Lampard made the signing of midfielder Alli a priority and believes he can rebuild a career that has stalled in recent years.
The 25-year-old, who has played 37 times for England, made six appearances under Spurs boss Antonio Conte after the Italian’s arrival in November.
The first £10m of his transfer fee will be payable after 20 appearances.
“I’m delighted to have signed for Everton, a huge club with a great fanbase and history,” said Alli, who scored 67 goals in 269 games at Spurs.
“I’m eager to get started and can’t wait for my first game in an Everton shirt.
“I’m looking forward to helping the team and the opportunity to work with the new manager Frank Lampard.”