The 23-year-old McIlroy, who started the final round with a three-shot lead, needed only 23 putts as he carded a flawless six-under-par 66 that gave him a 13-under total of 275 in the year's last Major.
The world number three sank a 20-foot putt from just off the green to birdie the par-four 18th in glorious late afternoon sunshine at Kiawah Island Golf Resort, then lifted his putter skywards in celebration.
"I don't think I have let it sink in yet but it was a great round of golf," the mop-haired Northern Irishman said after being presented with the Wanamaker Trophy. "I am speechless.
"It's been an incredible week. I had a good feeling about it at the start and I never imagined to do this."
His victory margin eclipsed the previous best set by golfing great Jack Nicklaus at the 1980 US PGA Championship in Oak Hill and underlined his burgeoning status as heir apparent to former world number one Tiger Woods.
McIlroy, who clinched last year's US Open at Congressional by a staggering eight shots, rattled up six birdies in a bogey-free display and will regain the number one spot when the world rankings are issued on Monday.
Britain's David Lynn, competing in his first US PGA Championship, birdied two of the last three holes for a 68 to finish alone in second.
Fellow Englishman Poulter, who briefly trimmed McIlroy's lead to one shot after a sizzling five-birdie start, faded after the turn en route to a 69 and a tie for third at four under.
Level with Poulter were his compatriot Justin Rose (66), Swede Carl Pettersson (72) and defending champion Keegan Bradley of the United States (68).
Pettersson, despite being slapped with a two-stroke penalty for grounding his club in a hazard on the first hole, responded well with three birdies in five holes before coming unstuck like so many others on the more difficult back nine.
Four-times champion Woods, hunting his 14th Major crown but his first in over four years, had to settle for a share of 11th place at two under after signing off with a 72.
Woods, who had been tied for the lead heading into the weekend for a second time in the last three Majors, said he had ultimately paid the price for a relaxed strategy going into the third round where he bogeyed four of his first eight holes.
"I was right there ... but I came out with probably the wrong attitude yesterday," the American world number two told reporters after offsetting two birdies with two bogeys in the final round.
"And I was too relaxed, and tried to enjoy it, and that's not how I play. I play intense and full systems go. That cost me."
Woods, however, paid tribute to McIlroy who he has long regarded as a player of uncommon talent.
"He's very good," he said. "He's got all the talent in the world to do what he's doing. And this is the way that Rory can play. When he gets it going, it's pretty impressive to watch."