The 23-year-old has spent the past two years away from Camp Nou, where he struggled for playing time in his younger days after featuring just six times.
Deulofeu has flattered to deceive at times during spells with Everton and Sevilla, but a loan stint with AC Milan last term proved profitable as he scored four goals in 18 games to earn links to his former club.
"I am very happy to be back at Barcelona," he told reporters. "It is my home and it was a shame I could not go back sooner. It is already decided. This year I will stay at Barca for sure.
"I am ambitious and I want to play with the best. I am very happy to have this opportunity that I have never had, to play in the first team of Barca."
Deulofeu played the full 90 minutes as Spain lost 1-0 to Germany in the European Under-21 Championship final on Friday night.