The 21-year-old, who spent a season on loan at Goodison Park in 2013/14, will officially join on 1 July and has signed a three-year contract, with an option for an extra season.
Everton manager Roberto Martinez said: “Gerard needs no introduction to anyone here, for we are all well aware of his incredible footballing talent.
“We got to know him really well from his loan period, not only as such a talented player, but also his great character. He will be a fantastic asset to our club.???
Deulofeu???s contract includes a release clause which kicks in if Barcelona make an offer to Everton meeting certain requirements within the first two years, and the Spanish side also have first refusal if Everton decide to sell.
Deulofeu impressed during his previous stint at Everton but then returned to Barca and subsequently spent time on loan at Sevilla.
He has represented Spain at multiple age-group levels, earning one cap for the senior side, and becomes Everton’s second signing of the summer, following the capture of Tom Cleverley from Manchester United.