The 22-year-old Marchand has taken his home Games by storm, starting with gold in the 400m individual medley before an unprecedented double in the 200m butterfly and 200m breaststroke.
Spurred on by a deafening crowd at La Defense Arena, he will chase another gold in the 200m medley, an event he won at the 2022 and 2023 world championships.
"It will be my last chance to experience a moment like this so I'm going to take it all in and give my all," said Marchand after qualifying fastest for the final.
American Caeleb Dressel will attempt to defend his 50m freestyle crown from Florent Manaudou, the Frenchman who won gold in London 12 years ago and has claimed silver at each of the past two Games.
Australia's Kaylee McKeown aims to make it a second straight Olympic backstroke double in the 200m, having already secured successive golds in the 100m.
On the track, US sprint star Richardson will look to live up to her billing as the women's 100m favourite, having missed the Tokyo Games after being banned for taking marijuana.
She must hold off Jamaica's Shelly-Ann Fraser-Pryce, the ageing five-time world 100m champion who is seeking her third Olympic gold in the discipline.
Richardson, who is trying to become the first US woman to win an Olympic 100m title since Gail Devers in 1996, said: "When I get on the blocks, it's about getting the job done. I know there's joy at the other end, at the finish line."
The first medals to be awarded on the track come in the men's 10,000m.
Three-time world champion Joshua Cheptegei of Uganda will be vying for his first Olympic title over the distance, having won silver at the Tokyo Games.
But competition will be stiff, with defending champion Selemon Barega one of three strong Ethiopians in the line-up alongside Yomif Kejelcha and Berihu Aregawi.
Gender row
Algerian boxer Imane Khelif's 46-second win on Thursday sparked a furious row about gender eligibility rules.
Italian boxer Angela Carini retired hurt and shrugged off attempts by Khelif to shake her hand, with Italian Prime Minister Giorgia Meloni saying the fight was "not on an equal footing".
The issue is likely to resurface Friday when Taiwan's Lin Yu-ting fights in the 57kg category.
Khelif and Lin were disqualified from the 2023 world championships, which were run by the International Boxing Association (IBA), but they were deemed eligible to box in the women's competition in Paris.
Both boxers also competed at the Tokyo Olympics three years ago.
The IBA said Lin and Khelif were disqualified from the world championships as "a result of their failure to meet the eligibility criteria for participating in the women's competition".
"The athletes did not undergo a testosterone examination but were subject to a separate and recognised test, whereby the specifics remain confidential," it added.
Novak Djokovic meanwhile faces a worrying wait to see if a knee injury will derail his tennis gold medal dream.
He is due to face Lorenzo Musetti in the semi-finals after Carlos Alcaraz plays Felix Auger-Aliassime.
Argentina can expect a hostile reception in Bordeaux for their men's football quarter-final against the hosts.
It will be the first meeting of the nations since Argentina players were recorded singing racist chants about their French counterparts as they celebrated winning the Copa America in mid-July.
