Brazil's Gabriel Medina won the bronze medal in the men's event with France's Johanne Defay finishing third in the women's.
The 22-year-old Vaast, who grew up in Tahiti's Teahupo'o and has caught some of the best waves of all time at the perfect reef pass, quickly established dominance and never gave it up, sparking celebrations on spectator boats in the channel and on shore.
"The dream came true. I can't believe it right now but I just made history - for me, for all Tahitians, for Polynesia and France," Vaast said, adding that he had lost his voice screaming back at local fans as he did a victory lap on a jet ski.
"A lot of people surf and it's part of our culture... I'm proud to say that surfing is born in Polynesia, so it means a lot for me."
As a Polynesian conch shell blew and a rooster - a symbol of France - ran around the presentation area, Vaast collected his gold medal in front of family and friends from the idyllic village in front of the wave.
Teahupo'o had delivered the greatest day of Olympic surfing competition last week but waves for the morning of finals day failed to live up to expectations, with long lulls and tricky winds.
Conditions improved as the day progressed and the men's finals were held in clean, if still infrequent, overhead barrels at "The End of the Road", as Teahupo'o is also known.
Vaast, sporting a mohawk haircut courtesy of his younger brother, drew first blood, scoring a 9.5 out of 10 after pumping through a long, deep tube.
Robinson followed with a slightly smaller version but came out after the wave spat a blast of water and air into the channel to score a 7.83.
Vaast quickly got another excellent score, an 8.17 for a tube followed by some searing turns to total 17.67 and leave the Australian chasing a near-perfect score.
Robinson had looked like the man to beat after knocking out Brazil's Medina and American John John Florence in earlier rounds.
But the West Australian, who employs meditative breathing techniques and named his first son Zen, could not manifest another wave to come and had to settle for silver.
Waves were infrequent for the women's final too, with a flurry at the end almost giving Weston-Webb enough to snatch victory from Marks.
"I'm just really happy and just trying to soak everything in because it's probably the best day in my life," a beaming Marks said, recounting the confusion as she waited to hear the Brazilian's final score, a 4.5 that came up just short and leaving her with a two-wave total of 10.33 to Marks' 10.50.
"Once they announced she didn't get enough I just burst into tears. Just super emotional - your whole life goes into a moment like this, so it's just really special," added Marks, paying tribute to her coach, Australian Luke Egan.
"I'm really grateful to have him in my corner. We looked at each other afterwards (and were) like, 'This is working out, world title, a gold medal', so we were pretty stoked."
Earlier, the women's semi-finals were filled with drama as Marks and Defay finished with their two-wave totals tied, the American squeaking through courtesy of the highest-scoring single wave.
In semi-final two, Brisa Hennessy suffered a brain fade and dropped in on Weston-Webb without priority, incurring a penalty that cost the Costa Rican all the points from her second scoring wave.
In a nerve-shredding men's semi-final, Robinson trailed Medina in sub-par conditions after the early exchanges, before capitalising on the only decent tube of the heat, punctuating it with an aggressive turn for a 7.83 out of 10.
Medina, with priority, then sat for 22 minutes waiting for a wave that never came, relegating him to the bronze medal battle.
The Brazilian was in no mood to repeat his fourth-place finish in Tokyo and claimed bronze with a two-wave total of 15.54 to Peruvian dark horse Alonso Correa's 12.43.
"It means a lot to me to be a medallist," said Medina. "This is something different for me - I think it touched the country (Brazil) more, the big page - a lot of people watching."
Already a superstar back home, Medina shot to new levels of international fame a week ago when a photograph of him seemingly levitating a metre above the water, arm extended and finger pointing to the sky, went global.
