His company, Power Corp., announced Wednesday Desmarais had died overnight, The (Montreal) Gazette reported.
Desmarais was one of the most powerful men in Canada, the newspaper said, with holdings that include Power Financial and three French-language newspapers: Le Soleil, Le Droit and La Presse. But he was also described as a very private man who generally stayed out of the public eye.
"If I have done nothing else in life I think I have proven that a French-Canadian can make it in the business community," Desmarais told the Gazette some years ago, summarizing his accomplishments.
Peter Newman, author of "The Canadian Establishment," had a more vivid description. Newman called Desmarais "a corporate gambler on a grand scale."
"He fit no stereotypes. He was like some rare breed of cat prowling the corporate jungles and free of the hidebound timidity that holds back would-be challengers," Newman said.
Desmarais was born in 1927 in Sudbury, Ontario. He left law school in 1951 to help his grandfather in a turnaround of the bankrupt bus company that is now Voyageur.
After he moved to Montreal in 1960, Desmarais began building up his business empire. He was still head of Power Corp.'s executive committee at his death, although he stepped down as chairman and chief executive officer in 1996.
Desmarais was also known as a philanthropist who served for years on the board of the Montreal Museum of Fine Arts. The French cultural center at Hebrew University in Jerusalem is named after him.
He was a companion of the Order of Canada.
Desmarais is survived by his wife, Jacqueline, two sons and two daughters. Power Corp. said the funeral will be private with a public memorial service to be announced.