The man — real name Raphael Graven, but known online as "Jean Pormanove" or "JP" — had built a following by putting on live internet shows in which he was abused or humiliated.
Prosecutors in the city of Nice said he died Monday in the nearby village of Contes.
Internet users said that the video — screened live on an Australian platform called Kick but widely shared afterwards — showed Graven lying immobile under a bed cover as one of two men in the room with him threw a plastic water bottle in his direction.
French government minister Clara Chappaz called the streamer's death an "absolute horror."
"Jean Pormanove was humiliated and mistreated for months live on the Kick platform," Chappaz wrote on X, adding that she referred the incident to French media regulators.
"The responsibility of online platforms regarding the dissemination of illicit content is not optional: it is the law," Chappaz continued. "This type of failure can lead to the worst and has no place in France, Europe, or anywhere else."
The Nice prosecutors' office said it had launched an investigation to determine the cause of death, and had ordered an autopsy.
Police in Nice have already for the past eight months been probing alleged "deliberate violent act" against "vulnerable people" that have been ending up as videos on the internet.
That investigation, started in December, sprang from a report by French outlet Mediapart revealing the existence of such videos, followed by thousands of viewers, especially on the Kick platform.
Asked about that investigation, Kick declined to provide any information, citing its policy of confidentiality.
The platform is seen as having less stringent user terms than those of its rival, the better-known Twitch streaming service.
Graven emerged on social media about five years ago and had about 500,000 followers on other social media platforms like TikTok and Twitch, Le Parisien reported. He was known for his gaming streams, "but also for extreme challenges with other streamers," the outlet reported.
Other social media influencers have been targets of deadly violence during livestreams in recent months.
In June, the Venezuelan prosecutor's office launched an investigation into the livestreamed murder of a popular TikTok user.
In May, the murder of a young influencer during a livestream in Jalisco, in western Mexico, shocked the country. Prosecutors opened an investigation for "femicide" after the murder of 23-year-old Valeria Márquez.
