A 41-year-old inmate died at the Nova Scotia Correctional Facility in Dartmouth on Sunday afternoon, according to the Department of Justice.
Guards discovered the man unresponsive in his cell around 4:30 p.m. and were unable to revive him.
Paramedics were called and the inmate was pronounced dead 15 minutes after he was found.
Police said no foul play is suspected.
The jail is a 272-bed facility housing both men and women.