Chinese divers had been targeting a sweep of all eight gold medals at the Rio diving competition, after winning six at the London 2012 Olympics.
But in Rio, China's Qin Kai and Cao Yuan had to settle for third, with a score of 450.21 compared to Britain's 454.32. The Chinese team, led by Qin, had held the men's 3 metre title since the Beijing Games in 2008.
Sam Dorman and Mike Hixon of the United States took silver after recording 98.04 - the highest score of the competition - for their final dive.
"We're so overwhelmed with what we've done," Laugher told reporters after the event. "The dream's happened."
China's Qin, who was widely expected to take home his third Olympic gold, said he was disappointed with his performance.
"I feel like I’ve let (China) down ... of course we don’t want this result," he said. "But since it’s like this, we can still gracefully lose, because our rival teams are also all very strong."
Brazil's Ian Matos and Luiz Felipe Outerelo failed to draw on the support of a vocal home crowd, splashing out in last place after posting a measly 28.8 in the second round.
Unlike diving venues at the previous two Olympics, Rio's Maria Lenk Aquatics Centre is open air, exposing competitors on Sunday to gusting winds and driving rain.
The centre's pool also remained a vibrant green despite assurances from Games organisers it would soon be back to its original blue colour after issues with the alkalinity of the water are resolved.
Mears and Laugher said the colour of the water had not impeded their performance and they had revelled in the "English weather."
"We embraced it, we embraced all the different things that were put in front of us and we've come out with a medal," Laugher said.
After recording a score of 86.58 in the fifth round for one of the most difficult dives seen in synchronised competition - a forward 2.5 somersaults with three twists - the British housemates said they felt lucky to even be competing in Rio.
In 2009, Mears nearly died after contracting the Epstein-Barr virus while competing at the Youth Olympics in Sydney.
"I've come from death's door to be here," he said. "So yeah, I'm pretty proud."
(Editing by Alison Williams and Andrew Hay)
