A 5.9-1 shot ridden by Thierry Jarnet, Treve is now undefeated in five races. She also won the Prix de Diane in June and Prix Vermeille last month.
"It was magical today because I had the luck to ride a great champion," Jarnet said.
Jarnet was picked to ride Treve after Frankie Dettori fractured his right ankle in a fall on Wednesday. The 46-year-old jockey also won the Arc with Subotica in 1992 and Carnegie in 1994.
Sunday's 92nd running of the Arc featured 17 horses from the start.
Japan hoped Orfevre would deliver the country's first Arc victory after narrowly losing to Solemia last year, but the gulf in class between Treve and the other horses was simply too big.
"When I saw Treve advancing, I followed her," Orfevre jockey Christophe Soumillon said. "With the effort she made, I thought I could catch up with her in the last 200 or 300 meters. But she is an extraordinary filly."