World number one Slingsby kept an eye on his only real rival, Cypriot Pavlos Kontides and finished just ahead of him, in ninth place, to win the gold medal.
As a huge crowd on the Weymouth peninsula cheered his win, Slingsby broke down in tears as he crossed the finish line before deliberately capsizing his boat with joy.
Kontides took silver while Sweden’s Rasmus Mygren finished in bronze.
“Words can’t describe how I feel right now. It’s been a long road. I’ve been through the highs and lows in the sport but nothing beats this,” Slingsby said after the race.
“The Olympics is a dream, it is the pinnacle of sport. Right now I’m the happiest man on the planet.”
The Aussie champion thanked his coach Michael Blackburn and his parents in an emotional speech.
“I have worked so hard and my coach and all my support staff so much,” he said.
“Blackers joined me after the last Games. I was sort of naturally talented but I wasn’t too professional and Blackers really helped me with my weaknesses and made me a lot more professional in my approach and the payoff is this, the best feeling in the world.”
Slingsby finished 22nd in the Laser class at the Bejiing Olympics, leaving him more determined than ever to win gold for Australia in the London 2012 Olympics.