The 30-year-old Frenchwoman won her first world title in 1987 at the age of just 10.
Having retired in 2006, it was only after a chance conversation that she discovered her childhood sport was about to become a medal event and decided to give it a second chance.
"This is really the result of two years of very hard work," she said after Friday’s gold-winning run.
Chausson's French team mate Laetitia Le Corguille won the silver while Jill Kintner took bronze for the US.
|Chausson took the women's gold 21 years after winning her first world title [GALLO/GETTY]
Latvia's Maris Strombergs won the men's event, avoiding two big crashes that left several riders splayed out on the course.
South African Sifiso Nhlapo crashed out in the curve after the biggest jump of the track and took out a few other riders, including highly fancied Jared Graves of Australia.
Nhlapo also got hit in the head by the wheel of one rider who managed to avoid a crash.
Speaking after the race Graves hit out at what he said was "stupid" riding on the part of some of his rivals.
"I'm pretty disappointed about how some of the other guys rode. I know they've got to be aggressive, it's the Olympic final, but they took themselves down in the process."
American Mike Day took silver and his team mate Donny Robinson won the bronze.
Strombergs said he hoped his win in the first Olympic BMX event would raise the profile of the sport.
"I come from a country where we only have 120 BMX riders," he said.
"I hope this achievement will make people sit up and take notice of us - and help us to get better."