The deal includes a buyout clause worth 35 million euros (£29.7m), the club said on their website.
A product of Barca's youth academy, Catalonia-born Deulofeu has played 35 matches for the B team this season, scoring 18 goals. He has also made four appearances for the first team.
Barca are in the market for another forward after they reclaimed the league title from Real Madrid this season but lost in the semi-finals of the Champions League for a second straight year.
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