"I went to bed at about 4 am and woke up at six wide awake," he said. "I woke my wife and said: 'I'm the Open champion. I can't believe I've done it.' She said: 'I can believe it, there's the trophy, now can you go back to sleep?'"
The Irishman, who has finished at least tied for fifth five times in three different majors and who was tied for seventh at this year's Masters, finally got his hands on the sought-after trophy by beating Sergio Garcia in a four-hole playoff at Carnoustie on Sunday.
Harrington thought his chance was gone after a double-bogey six on the 18th. But Garcia's par putt lipped out, and the Irishman holed a three-footer at the fourth extra hole to claim the title.
"I was just standing there, just thinking I was the Open champion," said Harrington, who ended Europe's eight-year drought in majors since Paul Lawrie won at Carnoustie in 1999.
Now, he is confident that the Europeans, who consistently beat the Americans in the Ryder Cup team competition, will start collecting more of golf's biggest prizes on a regular basis.
"I definitely think we have banished the hang-up for the moment," Harrington said. "European golf is very strong. This may be the start and, if it is, I will be telling people I started it."
Harrington wants to follow the example of Phil Mickelson, who won the Masters in 2004 after 46 majors without a victory before adding the PGA Championship in 2005 and the Masters again in 2006.
"I have always had it in my head that if I won one major I would want to win more," Harrington said.
Garcia, who was four strokes ahead of the field at one stage in Sunday's final round, is still waiting to win his first major after 36 attempts.
"He is probably the best ball striker in the game and he is still young," Harrington said. "I really felt for him. I know he is under incredible pressure to win a major, and he will. It will happen.
"The more he believes that the quicker it will happen. But the longer it takes the harder it gets. He could have left the field behind here and run away with it."
Harrington said when he was walking to the 18th green having twice played shots into the water known as the Barry Burn, he thought back to eventual loser Jean Van de Velde's triple bogey at the same stage in 1999.
"One big part of me making six was that it wasn't seven," Harrington said. "I was counting it up in my head. It crossed my mind that Jean took seven to lose the Open and I was sliding down that slippery slope too."
What: PGA Championship
Where: Southern Hills Country Club; Tulsa, Oklahoma
When: Aug. 9-12
Television: TNT, CBS-Ch. 12
Defending Champion: Tiger Woods