Nadeem, who was awarded life sentence in a murder case in Seemapuri, was found dead in his cell when the cell was opened this morning, Tihar Jail spokesperson said.
The reason behind his death is yet to be ascertained.
Jail authorities informed the police and the Magistrate about his death, and a judicial probe would be conducted into the incident.
His body has been sent to Deen Dayal Upadhayay Hospital for post-mortem.
Nadeem was apparently facing some family problems.