The attacker has moved to silence reports that he could be heading for the exit door by signing a contract that will keep him at Camp Nou for three more seasons
The new contract, which was agreed last week but only signed on Monday, ties the player to the team until 2016 and includes a £8.1 million (€10m) release clause.
"I’m very proud and I’m very happy, I’ve dreamed about this since I was a child," Tello said.
"I want to return the confidence to those who have confidence in me."
Tello made his first-team debut for Barcelona on November 8, 2011 in a Copa del Rey match against Hospitalet, scoring twice in a 9-0 rout.
The 21-year-old has so far made 23 appearances for the Catalans, scoring five goals in the process.