Subhan Anwar, 24, was jailed for murdering his partner’s two-year-old daughter Sanam Navsarka at a house in Huddersfield.
Sanam suffered 107 injuries at his hands during a month of shocking torture.
Two prisoners are being held by police on suspicion of murder after Anwar was found dead in a cell at the high-security Long Lartin prison, in Worcestershire, on Thursday.
Anwar was jailed for a minimum 23 years in 2009, while his partner Zahbeena Navsarka was found guilty of manslaughter and sentenced to nine years in prison.
Anwar and Navsarka, from Sheepridge, Huddersfield, tried to claim Sanam had stopped breathing after they left her alone in the bath for 10 minutes.
But Sanam was found to have 107 separate external injuries when she died.
Her tiny hand prints and bloodstains were found inside cupboards at the couple’s home in Huddersfield and at a former property in Batley.
As well as putting her in a tumble dryer, Anwar dumped her in the bin as her mother looked on.
Sentencing the couple in 2009, Judge Peter Thornton QC condemned their cruel and selfish treatment of Sanam and added that “humanity had let her down”.
The two prisoners being held by West Mercia Police on suspicion of Anwar’s murder are aged 45 and 47 and understood to be serving life sentences.
A force spokesman said: “West Mercia Police has launched a murder investigation after a 24-year-old man died in Long Lartin prison last night.
“The body of the man was found by prison officers just before 8pm on Thursday, February 14.
“Two men aged 47 and 45 have been arrested on suspicion of murder and are currently in police custody.”
Anwar was sent to Long Lartin, a maximum security prison near Evesham which holds up to 622 inmates who must be serving a minimum sentence of four years.
In a January 2012 report, chief inspector of prisons Nick Hardwick revealed that two rows of individual “bleak cages” were being used as a grim exercise yard for segregated inmates at the prison.
In August 2011, child killer Andrew Randall, who tortured and sexually abused his seven-week-old daughter Jessica, had his throat slashed by fellow inmates at Long Lartin but survived.
A Prison Service spokeswoman said two prisoners were in police custody following the death of Anwar.