Adrian Argent, 44, stood trial in the WA Supreme Court and was found guilty of murdering the mother of his two babies, then aged 14 months and one month, in May 2018.

The woman, who AAP has not named for cultural reasons, was punched to the ground, then forcibly kicked in front of a group of people in Kalgoorlie.

Argent then pulled her up by the hair and they walked back to their campsite where he struck her with either a 1.6m tree branch, a brick paver, or both.

She was unconscious for at least two hours and the assault caused bleeding on the brain, which eventually killed her, the court heard.

After the assault, Argent left but failed to obtain cannabis from an acquaintance, then visited his mother's house to get food before returning to the campsite.

When he realised she was not breathing, he called emergency services but she could not be revived, the court heard.

In his police interview, Argent admitted slapping the deceased as they walked home but denied any other assault.

During the trial, prosecutors alleged he did not intend to kill her, while his defence team claimed someone else was responsible.

Justice Joseph McGrath said the victim was highly vulnerable and should have felt safe with Argent.

"You did not have an intention to kill but you did have the intention to inflict an injury that was life-threatening," he said.

"This was not a pre-meditated attack on the deceased, but you were persistent on the night. It was not just one spontaneous act of violence."

The court heard Argent has a lengthy criminal record and a history of substance abuse.

"I accept that your background was characterised, particularly during your formative years, by dysfunction and disadvantage, which are all too often characteristics of Aboriginal offenders who come before the courts," Justice McGrath said.

"Your substance abuse and its role in your life reflects the socio-economic circumstances and the environments in which you grew up."

Australian Associated Press