Danjuma has prior experience playing in England, having been with Bournemouth for two years before he moved to Villarreal in 2021.
Everton were close to signing Danjuma in January before the Netherlands international opted to move to Tottenham Hotspur on loan for the rest of last season.
"I know I did not move to the club in January, that was because there was some uncertainty over the manager situation at that time, but I think it makes it even more beautiful for me to join now," Danjuma said.
"I am very grateful to be at the club and I can’t wait to play in front of the fans as well."
Everton finished 17th - one spot above the relegation zone - last season.
They begin their Premier League campaign with a home fixture against Fulham on August 12th.