Dupont's decision to join the Olympic seven-a-side team and chase gold this summer for the hosts had been in the works for two years.
Former World Rugby player of the year Dupont has been skipper under Galthie since November 2021, with the likes of flankers Anthony Jelonch and Charles Ollivon deputising when he has been absent.
For this year's Six Nations, which starts with France hosting Grand Slam champions Ireland in Marseille on Friday, Galthie has selected La Rochelle's No 8 Gregory Alldritt to lead his country.
"On the captaincy, we wanted to give life to our leadership, looking for other resources," former skipper Galthie told France Televisions on Sunday.
"Gregory Alldritt, he brings his own personality," the 54-year-old added.
Replacing Dupont in the number nine shirt, a highly prized playmaking position in French rugby, is Bordeaux-Begles' experienced Maxime Lucu.
Since making his debut in November 2021, 31-year-old Lucu has come off the bench 12 times in 18 Test appearances.
"Having Antoine Dupont in your position is like for the New Zealand fly-halves in the days of Dan Carter," Lucu told Monday's Midi Olympique.
"You know you're just going to play little snippets of matches.
"Instead of asking 10,000 questions, I preferred trying to understand what I could bring to those snippets of matches," Lucu added.
X-factor
Lucu's time in the set-up and his likely partnership with club team-mate Matthieu Jalibert this weekend puts the Basque half-back ahead of youngster Nolann Le Garrec in the pecking order.
"On the field, I can assure you that between Matthieu and me it can get heated," Lucu said.
"I shout, I am a pest, and I've insulted him during a match, like he can do to me.
"With Matthieu, we're like an old couple without the monotony," the former Biarritz scrum-half added.
A fluent English speaker thanks to his Scottish father Alldritt has helped his club to two straight Champions Cup titles under former Ireland fly-half Ronan O'Gara.
"He's quite chatty and speaks a lot," France and La Rochelle centre Jonathan Danty told reporters this month about Alldritt.
"Ronan O'Gara has made him the captain he is today, so he has a bit of an Anglo-Saxon vision.
"He demands a lot of accuracy and application, while keeping a smile at the same time and remaining a bit French," the midfielder added.
Not only is Dupont important to France on the field, he has also taken rugby outside the sports' traditional heartlands in the country, featuring on massive billboards and modelling for fashion brands.
During the World Cup, Dupont won a race against time to be fit for the quarter-final loss, with his recovery from a facial injury headline news captivating fans from the Pyrenees to Paris.
Over the next few weeks, Galthie and his team will be missing an individual who can win a game in a split second, as they plan to make up for the World Cup disappointment
"It will be very good for players to take their responsibility," former France winger Patrice Lagisquet told AFP on Monday.
"There won't be a responsibility on Antoine Dupont to be the X-Factor, there are other X-Factor players.
"Damian Penaud, Matthieu Jalibert, Charles Ollivon, Gregory Alldritt, Julien Marchand, Peato Mauvaka. There's (Louis) Bielle-Biarrey who is improving.
"It will be good that everyone takes some responsibility to have some initiative in the game plan. To show that it's not just Antoine Dupont is the difference," the 61-year-old added.
