The home hero, his name echoing around the land, did his best to stay grounded.
Now sharing the same territory as American greats Michael Phelps and Mark Spitz, the only other men to win four individual swimming golds at a single Games, Marchand marvelled at the comparison.
"That's crazy. Those guys are legends. Legends of their own sport," said the youngster whose coach, Bob Bowman, also worked with Phelps.
"It's just crazy to be compared to those guys. I don't think I realise from now. Maybe I will in a few days."
Marchand started the Games as a poster boy for the host nation's dreams and aspirations - a hero without any medals to his name, however.
He did not have long to wait.
The gold came in the first race, the 400 Individual Medley, and the Frenchman then pulled off the unprecedented feat of the 200 butterfly and breaststroke on the same day. On Friday he added the 200 Individual Medley.
"This morning I woke up and I was full of energy," Marchand told reporters.
"I don't think anything went wrong this week. It's been perfect.
"Four gold medals is not what I thought I could possibly do, I was trying to win one at first. I had four chances of doing it.
"Now I need this time to think about what I just did, for sure. So I need a vacation."
Bowman said comparisons with Phelps were justified.
"It's kind of proven that Leon joins Michael in that very rare club of people who, when the pressure is higher, they perform better," he said. "His performance rises to the pressure.
"There have been a lot of great swimmers. He's certainly one of the greats."
Duncan Scott, the silver medalist who also counts as one of Britain's greats after taking a record eighth medal for his country, agreed.
He's becoming a sort of global superstar now," said the Scot. "He kind of runs France now... you can see he's doing it with a smile on his face and the crowd's giving him so much energy. It's been amazing to witness."
