WARNING: This story contains details of violence some readers may find distressing.

A Perth man who murdered his partner by inflicting catastrophic head injuries on her, before setting her home on fire, has been sentenced to life in prison.

Former semi-professional basketball Chudier Towath Pal will have to serve at least 15 years in jail before he can be considered for parole.

He brutally bludgeoned mother of five Stephanie Lee Robinson at a house in Doubleview in January, 2021.

The Supreme Court had been told he had "crushed her skull" before returning to the home, dousing a mattress in an accelerant and putting it over Ms Robinson's body and setting it on fire.

Security cameras later captured him walking down the street carrying a blood-stained doona that he dumped in a bin.

Meth used before attack

Pal had unsuccessfully applied to be found of unsound mind, given he was suffering from an untreated schizophrenic disorder at the time.

But Justice Jospeh McGrath ruled he was ineligible to be excused from criminal responsibility because he had been using methylamphetamine when he killed Ms Robinson.

Pal, who played college basketball in the United States, was 206 centimetres tall, while Ms Robinson was only 164cm and of slim build.

Outside court, her distraught mother Nyomie Robinson said the sentence was too short.

"I'm glad it's finally finished … but I'm not happy with it," she said.

"She was a mother of five. My daughter."

Justice McGrath told Pal during sentencing he had considered all the factors, including Pal's personal circumstances, and given the seriousness of the crime decided it would not be unjust to sentence him to life in prison.

'Genuine remorse' shown

Despite the contention of Pal's defence lawyers, Justice McGrath disagreed he was a low risk of reoffending, given he would need to completely abstain from future drug use.

"I am satisfied that life in prison must be imposed," he said.

Pal sat mostly impassively during sentencing, and nodded as Justice McGrath explained his reasoning.

He set a non-parole period of 15 years for the murder and two years for the arson on the house, to be served at the same time and back dated to January 2021, when he was first detained.

Pal handed himself in voluntarily at Warwick police station where he told a police operator he had killed a person.

He had pleaded not guilty, admitting he had killed Ms Robinson but was of unsound mind and should be found unfit to plead.

Despite dismissing that, Justice McGrath found Pal had accepted responsibility for his crimes and expressed "genuine remorse".

He said Pal's mental health problems did mitigate his moral responsibility to some extent but his drug use exacerbated his behaviour.

Justice McGrath said Pal had believed Ms Robinson was part of a conspiracy to kill him.