The Catalan club held off a final-quarter fightback from defending champions Real to be crowned champions for a 17th time in front of their own supporters as they took an unassailable 3-1 lead in the five-game series.
Ante Tomic rose to the occasion with a 22-point haul and also claimed nine rebounds as the home side made up for the disappointment of losing their crown to Real last year by exacting revenge with a game to spare.
Captain Juan Carlos Navarro also maintained his impressive form with another important contribution of 14 points on a memorable night for Barca.
Real would have been eager to silence a partisan home crowd by making a strong start, but Barca led 25-19 after the first quarter and opened up an 12-point advantage in the second quarter when they raced into a 45-33 lead.
The visitors reduced the deficit to 47-41 at the halfway mark and trailed by only two points at 49-47 early in the third following baskets from Ioannis Bourousis and Tremmell Darden, but Real coach Pablo Laso was then ordered from the sidelines due to dissent.
The Catalans took a firm grip on the game as they moved into a 65-57 lead with a quarter remaining to stand on the verge of regaining their crown and looked to be coasting at 71-61, but Real refused to give up their title without a fight.
Barca's nerves appeared to be getting the better of them when Real fought back to make it 73-72 with only two and a half minutes remaining, but the hosts were not to be denied as they saw out the win to spark great celebrations.