Paul Laplante's body was found inside a penitentiary in east-end Montreal, where he was being detained while facing charges of first-degree murder.
The man's lawyer expressed shock at the news. He said his client had appeared ready to fight for his freedom.
"This is really surprising because when I saw Mr. Laplante last week he didn't show any particular signs of distress," Marc Labelle told The Canadian Press.
"He was a bit affected by the situation, for sure, but he was devoting his energy to preparing for his bail hearing. He wasn't showing signs of discouragement."
Laplante's spouse, Diane Gregoire, became a household name in Quebec over the course of a four-year disappearance. Her remains were finally found late last year.
Laplante, the former mayor of St-Liboire, Que., was arrested soon thereafter, on Dec. 13, 2011.
A court then ordered him to remain in custody and to refrain from speaking with the two children he had with Gregoire.
That's what troubled Laplante most, his lawyer said.
"He was particularly saddened by ... being unable to communicate with his children,'' Labelle said.
''That affected him. He respected the choice of his children — but that didn't please him. He was saddened by it."
He said his client also struggled to deal with the public opprobrium. His wife's disappearance was a prominent story in Quebec, and images of Laplante's eventual arrest were splashed all over the news.
"Let's just say there weren't too many voices rallying to his defence," Labelle said. "It weighed heavily."
Quebec provincial police wouldn't confirm Laplante hanged himself and they barely alluded to reports he was found dangling from the ceiling of his prison cell.
"He was found a certain way," said police spokesman Benoit Richard. "But is that what caused his death? These are things we'll see over the course of the investigation."
Police did not specifically identify Laplante but said a man of his age — 54 years old — was found dead in Riviere-des-Prairies penitentiary Monday.