Leeds Crown Court heard baby Luna had been left in the arms of Deane while her mum went to get some sleep on July 10.
Deane lost his temper during the night and subjected Luna to an attack when she continued to cry.
He admitted punching Luna to the face, squeezing her body and arms and shaking her.
Luna was taken to Leeds General Infirmary where she died in intensive care on July 14.
Today police said Deane had been found dead in his cell at the prison in Armley on Sunday.
The case was adjourned until Thursday when a hearing will take place at Leeds Crown Court.