An Australian "toy boy" convicted of murdering his Kiwi ex-girlfriend screamed "I've killed her ... I finally killed" after he drunkenly beat her to death, a court document has revealed.

Adam John Kennedy, 26, was sentenced in the New South Wales Supreme Court last month to at least 17 years in prison for the murder of former Hawkes Bay woman Debara Martin.

Ms Martin, 43, was found dead at a house in northern New South Wales on May 4, 2012.

The chef and mother-of-two had moved to Australia, where she worked as a kitchen hand and was recovering from breast cancer, two years before her death.

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She had met Kennedy, who a friend had described as her "toy boy", while she was a sex worker, but the couple had recently split before her death.

Justice Geoffrey Bellew's judgment, released this week, has revealed Kennedy screamed about killing Ms Martin on the night he beat her to death.

He arrived at his brother Luke's house about 11.30pm on May 3, 2012, and awoke his brother and a friend by yelling and knocking at the door.

"I've killed her ... I finally killed," he screamed, according to his brother.

Justice Bellew's judgment noted that in the months leading up to her death, Ms Martin told friends and family Kennedy had held a knife to her throat and hit her.

Police were told Ms Martin had suffered a black eye and swollen face but could not be convinced to report him.

The court heard the arguments between the couple centred on Ms Martin's decision to go back to being a sex worker.

On the night of the murder, a friend of the killer's brother, Brendan Ware, said he was so frightened of Kennedy's "drunken rampage mumbles" that he hid in a nearby paddock for several hours.

Luke Kennedy told police that on the scale of one to 10, his brother was drunk at a level of 11. He said his brother had asked him to help him dispose of Ms Martin's body but he had refused.

He went to police and reported the murder. Kennedy was later arrested driving drunk.

During his police interview, Kennedy told officers he had reacted to Ms Martin telling him to "get out of the house before I f***ing stab you".

After bashing Ms Martin, Kennedy phoned his father and said he had done something "really, really stupid".

The court heard he had intended to take her to hospital but when he reached the turn-off he became "overwhelmed with the prospect of being arrested".

Kennedy will be eligible for parole in June 2031.

- Additional reporting APNZ