Even in the relentless wind, Harrington managed to shoot 32 on the back nine to close with a 1-under 69 for a four-shot victory.
And to think he gave himself only a 75 percent chance of teeing off on Thursday, and only a 50 percent chance of finishing.
No one bothered asking him the odds of winning.
"I knew my game was there, but maybe this week I made the right decision at the right time, and got the right break at the right time," Harrington said.
He won last year at Carnoustie despite a double bogey on the final hole, beating Sergio Garcia in a playoff. This time, Harrington was afforded a pleasurable walk along the dunes of Royal Birkdale toward the 18th green, with the only suspense his margin of victory.
Harrington finished at 3-over 283, becoming the first European since James Braid in 1905-06 to win the Open in successive years. It was his first victory since the British Open last year, and moved him to No. 3 in the world.
"I'm quite enjoying this," Harrington said, cradling the claret jug. "I don't think I'll get down off the stage."
Norman, at 53 trying to become the oldest major champion, lost his two-shot lead in three holes and still had a one-shot lead going to the back nine. But he made eight bogeys in 30 mph wind and closed with a 77 to tie for third with Henrik Stenson (71).