The Aboriginal man was discovered unconscious in his six-person dormitory cell this morning by prison officers.
Efforts by prison medical staff and paramedics to revive him were unsuccessful.
Local police have attended the prison. There does not appear to be any suspicious circumstances.
The death will be subject to a Coroner’s Inquest, which follows every death in custody.
The Department of Justice, Corrective Services will carry out a review of the incident.
Corrective Services Commissioner Tony Hassall has extended his condolences to the man’s family and is travelling to Roebourne today.
Support will be offered to the family of the prisoner and other prisoners at the site.
In responding to this indigenous death in custody, the Department will seek cultural advice from community Elders.