The Senegal international signs a four-year deal with the Toffees who met the player's release clause at Aston Villa.
Despite Villa's terrible campaign last year, Gueye was one of a few players to salvage any pride from his performances and will add steel to Everton's midfield.
Everton boss Ronald Koeman expressed his delight with the signing of Gueye.
"Idrissa will provide quality in our squad in the midfield and we want to increase the quality in the team," he said.
"He was one of the players last season with the best record in interceptions and pressing in the midfield. We need this kind of quality and I’m happy to have him joining our club".