Chantal Sebire, 52, a former school teacher and mother of three, was suffering from an extremely rare form of cancer, which left her virtually blind, facially disfigured and in incredible pain.
She died at her home in the east of France on Wednesday only two days after a Dijon court had rejected her request for assisted euthanasia.
The cause of her death was not immediately known. A post mortem carried out on Thursday indicated that "her state of health did not lead directly to her death," Dijon prosecutor Jean-Pierre Allachi said.
The prosecutor also said that, "there were no specific factors that could have caused death," adding that a toxicology analysis would attempt to establish the cause of death.
Sebire's relatives had earlier opposed the carrying out of a post mortem. However, Allachi said the procedure was necessary as the "justice system had to know whether this was a natural death or someone helped the woman to die."
A Dijon court turned down on Monday Sebire's request to be given a lethal dose of barbiturates, ruling that it would contravene medical ethics and French law, which does not permit assisted suicide.
Her case revived the euthanasia debate in France after before-and-after pictures of her face were shown in the media. She also made a televised appeal last month, where she said that children ran away from her in fright due to her horrific appearance.
She said in her TV appeal for the right to die that, "One would not allow an animal to go through what I have endured," and that she had "come to the end of what she could suffer."
Her lawyer said Sebire, who was diagnosed with the disease eight years ago, was unable to take morphine for the pain due to the side effects.
Sebire suffered from cancer of the nasal cavity known as an esthesioneurblastoma, which is so rare that in the past 20 years only 200 cases worldwide have been reported.
Earlier this week media reports said Sebire was considering going to Switzerland to take advantage of euthanasia laws in the country. However, her lawyer said the woman would not have survived the trip.
Euthanasia is only legal in the Netherlands and Belgium. Switzerland has a system which allows people to die in the country on the condition that the patients themselves apply the lethal dose.
