An inmate died at Her Majesty's Penitentiary in St. John's on Saturday morning.
According to the Royal Newfoundland Constabulary, the 37-year-old man was found unresponsive in his cell shortly after 8 a.m.
Attempts to revive him were unsuccessful and he was pronounced dead at the scene.
Police also said there was no sign of foul play.
Several police cruisers and a hearse were spotted outside the prison shortly before 9 a.m.
Police and justice officials are continuing to investigate.
The victim's name has not been released.