The nerveless duo finished with 471.81 points having never dropped out of the top two and took the Olympic title 1.23 points ahead of China, with the Russian Olympic Committee third.
It is Daley’s third Olympic medal, after he won bronze in London and Rio, but his fourth Games after his debut in Beijing in 2008 as a 14-year-old.
“I mean to finally have this gold medal around my neck after so many – I mean I’ve been diving now for 20 years and this is my fourth Olympic Games and lots of people probably would have counted me out of this Olympics being the older person but I’m in the best shape physically and mentally,” Daley, 27, told the BBC.
“With the support of Matty coming into this competition and the way that we’ve been preparing, I think we’ve just had that unstoppable mentality this year and this is the first year that I’ve ever been able to think like that – that we are the ones to beat.
“I still honestly can’t believe what’s happening and I honestly didn’t think I would get there in the first place, but here we are.
“You want to win an Olympic gold medal but never think you actually will. I will carry on but I will definitely take a break. There are some beverages with my name on it to celebrate with my husband and family.
“This means an incredible amount. All athletes put in such hard work and dedication into our performances. To be an Olympic champion after four attempts at it feels extremely special.”
Lee added: “In 2018 I moved my whole life to London from Leeds, I had nothing really in London. Our aim was to get an Olympic medal and for it to go the way we wanted it to is awesome.
“I owe a lot to Tom because he has taught me a lot.”
The pair started well after an inward one-and-a-half somersault pike in the first round and continued their form to lead with two rounds left.
China’s poor dive – a score of 73.44 points was ranked sixth in the fourth round – left the route to gold open for Daley and Lee.
They scored 93.96 in the fourth round with an impressive backwards three-and-a-half somersaults pike to take charge.
A fifth dive – a reverse three-and-a-half somersaults tuck – earned 89.76 points to put the pressure on China ahead of the final round.
The British pair were 1.74 points ahead and an impressive forward four-and-half somersault tuck earned them 101.01 points and China could not catch them with their final effort.
The pair’s triumph came after swimmer Adam Peaty won Britain’s first gold of the Games with a dominant display in the men’s 100 metres breaststroke final.
Tom Pidcock then stormed to gold with a dominant ride in the men’s Olympic mountain bike race in Izu to make it a golden Monday for Team GB in Tokyo.