Unflappable Harman: The hunter who refused to be hunted on his way to Open glory
The American led the tournament by five shots after rounds two and three and by the end, he was six clear of his closest challengers.
"So pleased with the way I hung in there the last couple days," Harman told reporters.
"Got off to a bad start both days and turned it around, so really happy with that."
Rory McIlroy and Jon Rahm, the world numbers two and three, were among a pack of players who failed to reel Harman in, squandering opportunities when the world number 26 wobbled on a couple of occasions.
Starting his third round shortly after Rahm had completed a course-record 63, Harman dropped two shots in his first four holes.
He was not rattled, however, and a birdie at the fifth was followed by another at the ninth to quickly repair the damage.
Two more birdies followed on an error-free back nine to complete a round of 69 and restore his five-shot advantage.
"It would have been really easy to let the wheels start spinning and really kind of let it get out of control," he said.
"But I just kind of doubled down on my routine and knew I was hitting it well."
In heavy rain on Sunday, Harman again made two early bogeys and, with McIlroy off to a fast start with three successive birdies, the Hoylake galleries sensed that the leader might be wilting at last.
SMOOTH PUTTS
But Harman responded quickly, sinking smooth birdie putts on the sixth and seventh greens to bolt the door shut for the last time.
He negotiated the back nine without major alarms until he found one of the notorious pot bunkers around the 18th green.
The diminutive left-hander calmly chipped his ball out, however, and sank a par putt before hugging his caddy, removing his cap and acknowledging the applause from the packed stands.
Harman said he had always believed he could win a major but was worried he might have missed his chance.
"I'm 36 years old," he said. "Game is getting younger. All these young guys coming out, hit it a mile, and they're all ready to win."
Harman's performance to land his first major title was even more impressive because he only has two PGA Tour victories to his name, back in 2014 and 2017.
He also let the 2017 US Open slip from his grasp after leading the tournament at the end of round three, stumbling to a closing 72 as Brooks Koepka shot 67 to win by four strokes.
"It's been hard to deal with," he said.
"I think someone mentioned that I've had more top 10s than anyone since 2017, so that's a lot of times where you get done.
"So to put a performance like that together from start to finish was very satisfying."
