The Northern Irishman shot a final round 71 to finish 17 under par, two shots clear of Sergio Garcia and Rickie Fowler, and becoming only the third man to win three Majors by the age of 25- the other two on that list being Tiger Woods and Jack Nicklaus.
But McIlroy only completed his victory after surviving some nerve-shredding moments at the Royal Liverpool Golf Club as Garcia did his best to keep the excitement going to the end, the Spaniard trimmed McIlroy's lead from seven shots down to two at one point as he closed with a thrilling round of 66.
Rickie Fowler also finished in a tie for second place at -14 - though while Garcia pushed hard, Fowler was only ever hanging on during a poor shotmaking day, hoping for McIlroy to slip, and by the time he birdied three of the last four holes it was already too late for him to put pressure on his playing partner.
On a day of perfect conditions and outrageously good scoring, rounds in the 60s were the norm - indeed, McIlroy's 71 was the worst score of anyone in the top 10, with Jim Furyk, Marc Leishman and Shane Lowry all shooting final day 65s to make it into the top 10.
But the man himself was just happy to have done what it took to win on a day when his swing was not functioning as well as it had during his sublime three opening rounds of 66, 66 and 68.
"It feels incredible. Today wasn't easy, a few guys were making runs at me, so I just needed to stay focused and stay in the present," said McIlroy. "To have three legs of the four of the career grand slam at the age of 25 is quite an achievement.
"The lead never got less than two so I always felt like I had that cushion. Coming into the back nine I know I had holes where I could make birdie."
McIlroy also confirmed that his dad would collect on a £50,000 winning bet after ten years ago putting £100 on his son at 500-1 to win the Open by the age of 25.
"It doesn't matter to much to my dad any more, but I know to his friends [the three others who also put on the bet] I know they'll be thrilled!" he laughed.
At the start of the day, it seemed that nothing would induce McIlroy to blow his chance of glory as he birdied the opening hole in fine style to extend his lead to seven shots.
But back-to-back bogeys half-way through the front nine - including one on the easiest hole on the course, the par-5 5th - saw that lead trimmed, with Garcia going out in three-under-par 32 to close in - then eagling the 10th hole with an immaculate 230-yard approach shot.
McIlroy, however, responded in style. He produced birdies on the 9th and 10th to re-establish control, while Garcia lost momentum - and even needed a kindly ricochet off the stands on the 12th to save par.
McIlroy bogeyed the 13th after an atrocious tee shot on the par-3 to put himself back in jeopardy - but when Garcia's birdie putt on the 14th shaved the edge of the cup, and he left his bunker shot on the 15th in the sand, the tournament was as good as over.
Garcia birdied the downwind par-5 16th, but unforgivably left his 15ft birdie putt short on the 17th after a superb approach shot.
McIlroy birdied the 16th after two perfect shots to the green of the par-5 - he later described it as "the hole that settled the championship" - then showed one final sign of nerves with a loose approach into the rough on the 17th, a mistake he rectified with a perfect chip recovery to 12 inches.
That shot gave him a par, and guaranteed him the luxury of enjoying a victory procession up the final hole as he became the Open champion, and the second Open champion from Northern Ireland in the space of three years.
It also gives McIlroy the third leg of a career grand slam - and given that the layout at Augusta arguably suits his game better than any of the other Majors, he will be a prohibitive favourite to finish the set next April.
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