Doctors at Ancona's Salesi paediatric hospital on the Adriatic coast declared the 22-month-old brain dead late on Saturday, three days after her father returned from his university teaching job to find her barely breathing.
The child, Elena Petrizzi, had surgery to relieve swelling on the brain, but doctors said it was too extensive to save her.
Prosecutors will decide whether to charge the father, Lucio Petrizzi, with manslaughter.
The distraught Mr Petrizzi has told police his memory went blank and that he thought he had dropped the child off at nursery on his way to work as professor of veterinary medicine at Teramo university. When he found the child after finishing teaching, he frantically called for an ambulance.
The child's mother, Chiara Sciarrini, fighting back tears as she read a message on television, appealed for understanding for her partner, whom she described as being distracted while juggling many responsibilities.
"I want to shout to the entire world how much my companion loved his daughter, he is an exemplary father," said Ms Sciarrini, a university researcher who is eight months pregnant. "What happened to him could happen to anyone."