The 17-year-old agreed a £2.2 million switch to Camp Nou in March - though the fee will rise in line with first-team appearances.
Halilovic will begin his Barca career in the club's B team, competing in Spain's Segunda Division.
The attacking midfielder is Croatia's youngest international having made his debut against Portugal in June 2013, though he was not selected for Niko Kovac's FIFA World Cup squad.
Halilovic has two years' worth of first-team experience under his belt with Dinamo, helping them to Croatian First League titles in each of the past two seasons - their eighth and ninth successive domestic triumphs.
"It is a great day, I'm very happy," he told Barca's official website. "I'm a Barca fan and always know everything about the club
"I speak a little Catalan. I am very pleased to have been given the opportunity to play for the greatest club in the world.
"A big salute to all the fans and the club, long live Barca."
