An inmate from the Nitzan Detention Center was found lifeless in his cell on Wednesday morning, Israel Prison Services reported.
He was found lying on the floor unconscious with no pulse.
A medic and a doctor arrived on the scene and began resuscitation attempts but were forced to confirm the death of the prisoner. His family has been notified.
The prisoner, a resident of east Jerusalem, was sentenced to 18 years for murder in 2017. This was his third imprisonment.
Police are investigating the incident.