James Sullivan, 27, from Nottingham, was serving a 20 year sentence at HMP Lowdham Grange for murdering Sara West at her home in Aspley after a row about their nine-week-old child in 2010.
The Prison Service has confirmed that Sullivan was found “unresponsive” in his cell on Thursday, March 24.
A spokesman said: “Staff attempted CPR and an ambulance was called but he was pronounced dead at 8.34am.
“As with all deaths in custody there will be a investigation by the independent Prisons and Probation Ombudsman.”
A file is being prepared for the coroner.