Humbert, 22, died Friday morning, two days after Marie Humbert allegedly injected her son with barbiturates during a hospital visit. His death revived a debate in France over an age-old taboo, legalizing euthanasia.
In Western Europe, only Belgium and the Netherlands permit mercy killings, but within a strict legal framework.
Humbert's mother said she wanted to give her son the gift of "death, after having given him life" and defied the law to do so.
However, the plan went askew. Marie Humbert was detained by police for questioning Wednesday as her son slipped into a coma.
Breaking with a tradition of medical discretion, doctors said Friday that they had decided to limit "active treatment" of the young patient. He died hours later.
Vincent Humbert was severely disabled in an auto accident in 2000 and spent three years at a hospital in the Normandy town of Berck-sur-Mer, the first nine months in a coma.
Only the thumb of his left hand was mobile. He communicated through an arduous system of thumb pressure in response to letters of the alphabet.
Over time, the young man understood that he did not want to go on living.
In November 2002, Humbert beseeched President Jacques Chirac to accord him the right to die. Chirac wrote and telephoned him in the hospital but explained he could not comply. Humbert eventually mounted a death plan with his mother and painstakingly wrote a book explaining his case.
His mother allegedly executed the plan to end her son's life on the third anniversary of his accident and the release day of the book, "Je vous demande le droit de mourir"' (I Ask You for the Right to Die).
Days before, she had told newspapers that she and her son had "a plan."
"I'm really happy, happy that my brother is finally free," said younger brother Laurent Humbert on LCI television. "It's an enormous relief."
However, the death of Vincent Humbert puts the political establishment face-to-face with the question of whether to legalize euthanasia.
"This debate is not closed, and we must resume it without prejudices," Health Minister Jean-Francois Mattei said.
The word euthanasia is not even mentioned in French law. It comes under various headings, from "voluntary homicide" to "murder" or "failure to assist a person in danger."
Marie Humbert risks being placed under investigation in the death of her son in one of these categories.
However, Justice Minister Dominique Perben asked the prosecutor's office to "apply the law with the greatest humanity to take into account the suffering of the mother and the young man."
In an unusual move, two lawmakers representing France's two main political rivals, the governing Union for a Popular Movement and the Socialist Party, said a change in the law was "indispensable."
"We cannot let this gap between the law and reality endure,'' said Gaetan Gorse, the Socialist, and Nadine Morano of the center-right party.
Many doctors in France, after consulting with families, are known to discretely stop treatment for some patients in extreme suffering and with no hope of being cured, a form of "passive euthanasia."
Humbert's medical team said it limited his treatment after a "collective and difficult" decision, said Frederic Chaussoy, head of intensive care at the Heliomarin Center where the young man was treated.
"In my mind, we quickly need to legislate on these problems," Chaussoy said on RTL radio. "You can't ask a doctor to resolve these problems."
By Elaine Ganley