The man, who cannot be named for legal reasons, was charged after the girl was found dead in her room at Aberglasslyn, a suburb of Maitland, in the early hours of September 23, 2015.

She had been bashed by her stepfather and put to bed, where her body was discovered by her mother at about 5.45am.

The man pleaded guilty in the NSW Supreme Court in Sydney on Wednesday, appearing via audio-video link from South Coast Correctional Centre.

He remained silent throughout his court appearance, except to say "Yes, your honour", "Guilty" and "Alright, thank you."

Justice Peter Hamill formally entered the conviction.

A sentencing hearing for the man will be held in Newcastle on February 26.

The girl's mother has also been charged over the death, after she allegedly failed to intervene while her daughter was being bashed.

She appeared in the same court, watching in the public gallery as her partner entered his guilty plea.

When it was time to enter her plea to manslaughter, she stood at the back of the court room and responded: "Not guilty."

The court heard the mother will argue she was under duress and suffered from battered wife syndrome at the time her daughter was murdered.

She will face a two-week trial at Newcastle beginning on March 5 next year.