The 22-year-old staved off five break points in the first set, including three in his third service game as the American made a terrific fist of dealing with the booming Kyrgios delivery.
But the Australian third seed held his nerve and pounced at his first opportunity, a pair of forehand passing shots earning the decisive break before an ace sealed the first set in 37 minutes.
Twice Kyrgios thrilled the crowd with delightful touch at the net, while he used angles from the baseline and the occasional flat forehand to throw the 25-year-old off his game.
A free-moving Kyrgios then cranked the pressure to another level in the second set, getting more balls in play on the world No.47's serve as he eyed an early kill.
A Harrison double fault to concede serve was telling of that intensity and a double break was more than enough security for a man who had only dropped serve three times all tournament.
Again playing with his left knee strapped, Kyrgios' fitness will come under the microscope ahead of the season's first grand slam.
At one stage in the first set he told the chair umpire that "it is an injury which could keep me out of the Australian Open", when denied a medical time-out.
"That rule should be changed ... it's getting worse," he said.
Kyrgios only got better from that point on though, a 17th ace sealing the victory in 1 hour and 13 minutes as he appeared largely untroubled in his movement.
"I've got fond memories of Brisbane, played Davis Cup here and had a massive win over the US," Kyrgios said after the win.
"Coming here all week I felt right at home ... I love playing in front of you guys even though sometimes you may not see it that way, but I do."
In lifting the Roy Emerson Trophy, Kyrgios becomes the second Australian champion in the tournament's 10-year history after Lleyton Hewitt in 2014.
The triumph, the fourth of his young career, lifts Kyrgios four spots to No.17 in the world ahead of this month's Australian Open.
His form in that match, plus his comprehensive disposal of Harrison in the decider will mean that he will arrive in Melbourne as a legitimate contender if his body holds up.