James enjoyed a brilliant all-round game, posting a triple-double with 26 points, 11 rebounds and a game-high 13 assists and was named most valuable player of the series as he finally won an NBA crown in his third trip to the finals.
As the clock ran down, James joined in with the deafening celebrations in the AmericanAirlines Arena from the sidelines, jumping and waving as he roared along with the fans with a beaming smile as the seconds ticked away.
"This means everything," he said after handing off the golden NBA Championship trophy to accept the MVP award from Boston Celtics great Bill Russell as confetti rained down from the rafters.
"This is the happiest day of my life."
The 27-year-old James was dominant throughout the series but in the Game Five clincher, he had help from all his cohorts.
Six Heat players scored in double figures, including Chris Bosh with 24 and reserve Mike Miller with 23, who went 7-of-8 from beyond the three-point arc in a spectacular display of shooting for the Heat.
Miami's confidence soared as the game went on, as they made a sizzling 14-of-26 three-pointers to tie the record for most long-range baskets in an NBA Finals game.
The Heat led 31-26 after the first quarter, extended the lead to 10 by halftime and then used a blitz of 16 points in a row in the third quarter to open up a massive 25-point lead that sent the rowdy, standing-room only crowd into early delirium.
Three-times NBA scoring champion Kevin Durant led the young Thunder team with 32 points with Russell Westbrook and James Harden adding 19 points apiece for the losers.
James, three-times league MVP, gave Durant a long embrace as the buzzer sounded to end the game and the series.
"I'd like to congratulate the Miami Heat," Thunder coach Scott Brooks said. "They did a fantastic job. We ran into a team that was tough to beat tonight."
It was Miami's second NBA title following a 2006 triumph and erased the bitter taste of a six-game defeat by the Dallas Mavericks in last year's Finals.
James averaged 28.6 points, 10.2 rebounds and 7.4 assists in the series for Cleveland, who were swept in four games in 2007 by the San Antonio Spurs, and then lost in six to the Dallas Mavericks last season.
"Losing the finals last year put me back in place, it humbled me a lot," said James, before succumbing to the excitement. "It's about damn time!"
Heat coach Erik Spoelstra said coming back to win the title this year was gratifying.
"We remember last year, we wanted to make up for last year," the coach said. "We had confidence in what we could do."
Dwyane Wade, who was MVP of the championship series in 2006 when the Heat won their first NBA title, said: "We had so much pain, so much pain, so much embarrassment from last season.
"Nothing had to be said. We were on a mission and that mission was not completed until tonight."
The Thunder, the second youngest team by average age to compete in an NBA Finals, had battled the Heat through to the finish of each of the first four games but were overwhelmed in the end by the determined home team.
"It hurts. It hurts, man," said the 23-year-old Durant. "It just hurts to go out like this. We made it to the Finals, which was cool for us, but we didn't want to just make it there."
Oklahoma City coach Scott Brooks said he was proud of his team.
"I just told the guys, we didn't win a championship this year, but they gave it a championship effort all season long. It's something I'm proud of. I love our guys."