Deulofeu scored 18 times in 33 matches for Barcelona's B side last season and also made a handful of substitute appearances for the Spanish champions.
The 19-year-old was rewarded with a long-term contract earlier in the close-season, but Barca are willing to loan him to Everton in a bid to further his development.
Martinez has moved quickly to secure the teenager's services, making his fourth signing after previously raiding his former club Wigan for striker Arouna Kone and defender Antolin Alcaraz, as well as landing Atletico Madrid goalkeeper Joel Robles, who was on loan with the Latics last season.
"Gerard is a real diamond of Spanish football and a boy with incredible footballing talent and I am delighted that he has chosen to take the next step of his career with Everton," Martinez told Everton's website.
Deulofeu is a graduate of Barcelona's famed La Masia academy and has played for Spain's Under-17s, Under-19s, Under-20s and Under-21s.
He will join up with the Blues squad later this summer as he is currently on a break after involvement in the Under-20s World Cup in Turkey.