The 19-year-old attacker, who was part of Spain's squad for the Under-20 World Cup in Turkey, scored 18 times in 33 matches for the Catalan club's 'B' team.
|22/1||Everton are 22/1 with Coral to finish in the top four
Deulofeu made one appearance in La Liga last season, coming off the bench against Mallorca, and also featured in Champions League group stage ties against Spartak Moscow and Benfica.
But the Masia academy product's game time was expected to be limited next season following Barcelona's capture of Brazilian superstar Neymar.
The Blaugrana loanee is Everton's fourth signing of the summer transfer window, having already secured permanent deals for ex-Wigan trio Arouna Kone, Joel Robles and Antolin Alcaraz.