A Bunbury man who murdered a stranger during a frenzied attack outside a cafe in Western Australia's South West has been sentenced to life in prison with an 18-year minimum.

Saxon Steele Vitali, 25, pleaded guilty to murdering 56-year-old Glenn Howell, who was set upon outside the cafe in the town of Kirup on the evening of July 14 last year.

Vitali's attack on Mr Howell lasted more than half an hour, during which he suffered severe head injuries. He died in hospital 11 days later.

The Supreme Court heard that after an altercation between the pair, Vitali had started calling Mr Howell "a dog" and kicking Mr Howell's car.

Mr Howell was chased by Vitali, and pleaded for help from the cafe staff as he tried to defend himself.

At one point Mr Howell crawled under his car to try to escape from Vitali, who then dragged him by his legs back out into the open.

Vitali also stomped on Mr Howell's head as he lay on the ground.

Justice Michael Corboy said it was an act of "gratuitous and inexplicable violence".

No history of violence

The Supreme Court had been told that Vitali was extremely drunk, could not recall how the fight started and could not explain his actions.

Vitali, a forklift driver, had struggled with alcohol and drugs — including methamphetamine — over several years, the court heard.

In sentencing Vitali, Justice Corboy said he had to take into account the facts that he had surrendered himself to police, had pleaded guilty at the first reasonable opportunity and had no history of violent offending.

Vitali had no history of violent offending, the court heard. ( Facebook: Saxon Vitali )

He told the court he accepted Vitali was remorseful, "in fact devastated," by his actions and had written to Mr Howell's family.

But Justice Corboy said "senseless and gratuitous violence in public places is a significant problem" and there needed to be deterrence.

The 25-year-old was also given an 18-month jail term for damaging Mr Howell's car, to be served concurrently

Vitali's sentence was backdated to July 19.

Outside the court, Mr Howell's older sister, Linda Gillon, said she welcomed the sentence.

"Maybe now my brother can rest in peace," she said.

"I mean you can't put time on it. I'm grateful … it's finished."