François-Xavier Leuridan, known as FX, was hit by a car early on Tuesday morning in the small village of Bouée on the Atlantic coast.
Prosecutors said evidence from four witnesses suggested he had thrown himself in front of the car.
“The 22-year old man committed suicide by throwing himself into the path of a vehicle just a few minutes after another car had managed to miss him,” local prosecutor Sylvie Morin told newspaper Presse Océan.
Secret Story has been running on TV channel TF1 since 2007. Leuridan cut a striking figure in the third series in 2009 with his long hair and androgynous features.
He cultivated a confrontational and extravagant personality that irritated his housemates but brought him a wide following with viewers. He lasted until the penultimate week of the show, going on to use his popularity to launch a music career with the single 'Luxury'.
Fellow contestants expressed their grief in interviews and on Twitter.
“RIP FX, even if you were completely mad and unbearable I loved you. I can’t stop crying,” wrote one on Twitter.
Another told newspaper France Soir that Leuridan “was someone who hated being alone. He was a baby, even if the media saw him as irritating.”
Leuridan, who was reported to have been suffering from depression, appeared on another reality show, Carré Viiip, earlier this year. The show was cancelled before completing its run due to low audience numbers.