Clarke carded a final round of 70 in tough conditions to finish three shots clear of American pair Phil Mickelson and Dustin Johnson, with Denmark's Thomas Bjorn a shot further back in fourth - eight years after he blew a three-shot lead here with four holes to play.
"It's just incredible, I don't know what to say. I'm speechless," said Clarke, who lifted the Claret Jug at his 20th attempt. "I played okay today, I did what I needed to do.
"The last couple of holes I was trying not to make any stupid mistakes. I just tried to play really carefully and it was good enough to win."
Clarke was playing the 54th major of his career and had not had a top 10-finish in them for a decade, but did claim his 13th European Tour title in Majorca in May.
"I won six weeks ago and the more you put yourself in winning positions the more comfortable you get with it and I've been very comfortable with myself this week," Clarke added.
Clarke's wife Heather died in 2006 after a long battle with cancer and the Ulsterman dedicated the win to their sons Tyrone and Conor.
"It's for the kids," an emotional Clarke said. "They played Royal Portrush this morning and were watching on TV."
As for the celebrations, Clarke added: "I think they will be very, very long and I'll be very hungover."
Speaking at the prize-giving ceremony, Clarke added: "It's been a long and bumpy road, I have had some good things happen to me and some bad things, but I've had so much support from an awful lot of people.
"I'd like to thank my parents and my fiancee Alison, and there's someone up there watching as well. To everybody, thank you very much."
Clarke is the third member of the International Sports Management (ISM) stable to win a major this year, following the victories of Charl Schwartzel and Rory McIlroy in the US Masters and US Open respectively.
And the head of ISM, Andrew Chandler, added: "There is a lot of talk of success and they will be trying for the clean sweep (at the US PGA Championship).
"Darren has had a lot of shots at it and you know time might be running out, and then it all happens."
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