The 46-year-old mobster was found unconscious in his cell shortly after midnight at the federal penitentiary in Donnacona, Quebec. Prison staff attempted to resuscitate De Vito before transporting him to the hospital, where he was pronounced dead.
An investigation is underway to determine the cause of death.
De Vito — associated with the Rizzuto crime family — was arrested in 2010 and convicted of conspiracy to import drugs and gangsterism. He began serving an 11-year, seven-month sentence on June 20, 2012.
Judge Isabelle Rheault concluded that De Vito was a major link in the criminal organization and part of a small circle of Mafia insiders.
Wiretapping and surveillance evidence presented by the Crown showed De Vito had connections to the most powerful members of the Rizzuto clan, who were running an international cocaine import operation.
De Vito managed to escape the sweeping anti-Mafia operation dubbed "Operation Coliseum" in 2006, and was on the run for four years before being arrested in the Montreal borough of Saint-Leonard in October 2010.
De Vito was the husband of Adele Sorella, who is in prison for killing their two daughters while he was on the run. On June 24, she was convicted of the first-degree murders, which were committed in March 2009.