The Correctional Service of Canada says Grant Valouch was found unresponsive in his cell at the Pacific Institution on Sunday and he couldn't be revived.
Valouch was serving an indeterminate sentence for the second-degree murder of Randall Lanthier in May 1990.
He was originally charged with first-degree murder, but was found guilty of the lesser charge at the end of a Winnipeg trial in 1991.
No cause of death has been released for Valouch, who was 49 years old.
Corrections Canada says it will review the circumstances around the death, and both police and the coroner have been notified.Suggest a correction