The inmate was identified as Akhilesh Kumar, a resident of Gurugram's Darbaripur village.
"He was ill for the last few days and was referred to civil hospital after he complained of a breathing problem," the official said.
A magisterial probe has been ordered into the "mysterious death", as claimed by Kumar's family.
According to the police, Kumar was arrested in 2012 for his involvement in a murder.
A district and sessions court sentenced him to life imprisonment in 2013.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)