Last to descend in the final after his superlative semi, he flashed through the course to finish more than five seconds ahead of Britain's Adam Burgess, who took silver, with Matej Benus of Slovakia securing the bronze.
"I don't know what to say, it's better than my dreams, it's my best race of my life," a delighted Gestin said.
"Everyone on my team, my mentor, my brother and I, wanted it. When I crossed the line, I knew I had put in a great run, and now I'll just enjoy it."
It was an afternoon of high drama on the stadium's white water as the last 12 paddlers fought it out for the medals, with thrills and spills aplenty before Gestin stole the show.
Fourth out of the 12 athletes in the final, Senegal's Yves Bourhis looked to have sensationally taken the lead after a hair-raising run, but the judges hit him with a 50-second penalty for missing the ninth gate that quickly dashed his hopes after he passed the finish line.
Tokyo gold medal-winner and world number two Benjamin Savsek of Slovenia suffered a similar fate when he clattered into the fifth gate, incurring a 50-second penalty for not going through it correctly.
There was also agony for Ireland's Liam Jegou, whose brilliant run was ruined by touching the 23rd and final gate on the course to drop him from first to third with five paddlers to come after him.
The tide of luck began to turn when Briton Burgess thundered through his run to go into top spot before Germany's Sideris Tasiadis and Miquel Trave of Spain came up just short.
After out-classing the field in the semi-final, Gestin threw himself at the course and put on a display of incredible skill, speed and power, executing a flawless run that ended in a glorious gold medal.
