The 32-year-old produced a devastating acceleration at the start of the second of seven laps around the dusty 4.4km circuit on Elancourt Hill and rode solo to victory.
Haley Batten of the United States and Jenny Rissveds of Sweden were involved in a fierce scrap for silver, with Batten bursting clear to finish runner-up, two minutes 57 seconds back.
Young Dutchwoman Puck Pieterse was the only rider who looked capable of making it a race and was alone in second place when she suffered a puncture on lap five and needed a wheel change.
She fought back to finish fourth ahead of Britain’s former world champion Evie Richards.
Ferrand-Prevot, who will return to road racing after the Olympics, is a five-times cross-country world champion but suffered heartbreak at the last two Olympics when favourite.
She failed to finish the race in Rio de Janeiro and in Tokyo she crashed and suffered a puncture, coming in 10th.
It was little wonder then that the tears were flowing after she reigned supreme in the hills near Versailles, embracing her team and family and pretty much everyone else in the chaotic finishing area.
After receiving her medal she made her way through a long line of TV and media interviews before holding up the tricolore flag towards hundreds of chanting fans, making a heart with her hands and closing her eyes to let the moment sink in.
“After so many years and after so much hard work, winning today was like a dream day,” she told reporters. “I was on a mission today. After the warmup I knew it was my day today.
“On the last lap I knew I had a huge gap so I was slowing down because I was saying ‘You don’t have to make a mistake’.
“I was flying today.”
Initially it looked like being a proper battle for gold as Ferrand-Prevot, team mate Loana Lecomte, Pieterse and Austria’s Laura Stigger formed a four-rider breakaway.
But as they began their second circuit, Ferrand-Prevot sped off the front in a blaze of dust.
In hot conditions her only mistake was failing to grab a bottle of water from the feed zone as she started her final circuit but apart from that she was faultless.
After powering up the final climbs and safely down the boulders on the descents she could finally relax and start celebrating as she rounded the final corner and into the straight, where Paris Games chief Tony Estanguet joined the throng roaring her across the line.
While it was glory for France, it was also a momentous day for Batten, who recorded the best result by an American in Olympic mountain biking despite breaking a wheel.
“She’s been waiting this for a long time, so happy for her in her home country,” the 25-year-old said, referring to Ferrand-Prevot.
“Next Olympics it’s mine!”