Kenneth Haupai Mathew Smith bit a woman after becoming frustrated at being locked out of the house.
Smith pleaded guilty to contravening a protection order and common assault when he appeared in the Whanganui District Court on Tuesday.
"He had been drinking so she locked him out," Smith's lawyer Richard Leith told the court.
Smith and the victim shared responsibility for four children they had together, Mr Leith said.
"The situation was he had expected to be able to come there because he was looking after the children the next day. She locked him out because he had been drinking.
"He climbed in the window, lost his cool with her and ended up biting her.
"He knows he needs to look at his drinking."
Judge Dugald Matheson convicted Smith and remanded him to November 28 for a pre-sentence report.
"I want to get some good assistance in place so that you're not exposed to reacting in a way that unfortunately happened there."