Nathaniel Jackman has pleaded guilty to multiple charges relating to an ute rollover in the Midwest which killed a baby and two women in 2024.
His defence lawyer said Jackman had been forced to drive, despite not holding a licence.
Jackman is due back in the Geraldton District Court for sentencing next year.
A last-minute guilty plea by the man behind the wheel has halted a trial over an ute rollover that killed a baby and two women in Western Australia's remote Midwest.
CONTENT WARNING: This story contains the names and images of people who have died.
Nathaniel Jackman was driving a Toyota Hilux, with five passengers on board, when it rolled on the Geraldton-Mt Magnet Road near Yalgoo, about 500 kilometres north of Perth, just before 11pm on August 10, 2024.
A weeks-old baby, Levi Ashwin, died at the scene from multiple injuries including skull and rib fractures, along with Gabrielle Brockman, 21, who suffered a head injury.
Levi's mother, 33-year-old Marrika Brockman, later died in hospital from a head injury.
Jackman, 24, had been due to face trial in the Geraldton District Court on Monday, but pleaded guilty to three counts of driving causing death, and two of driving causing grievous bodily harm.
The court heard Levi's father, Dwayne Ashwin, and another passenger, Jeffrey Incich, were seriously injured and would have died without medical intervention.
Prosecutors said Mr Incich was permanently disabled as a result, and now requires 24 hour support.
There was no infant car seat and the passengers were not wearing seatbelts.
The court heard the ute had travelled on the wrong side of the road and onto the verge for 70 metres before Jackman adjusted the wheel.
Prosecutors said Jackman had never held a licence, was driving tired and had too many passengers in the car at the time of the crash.
Police said blood pooling indicated four passengers were ejected at the start of the rollover.
A blood sample taken from Jackman tested positive for THC at the time of the crash, with the levels suggesting the then-22-year-old smoked cannabis the same afternoon.
Defence lawyer George Guidice said Jackman had been forced to drive, despite saying he could not.
Mr Guidice said the group had travelled from Kalgoorlie to Meekatharra the day before the crash for a funeral.
He said there had been arguments after the funeral, with some of the group keen to stay another night, and others wanting to drive onward to Geraldton.
Mr Guidice said Dwayne Ashwin drove around 230 kilometres, past Mount Magnet, before Jackman to take over.
He said Jackman refused, but Mr Ashwin was "very forceful and insisted", adding that he become angry and started swearing.
Mr Guidice said Jackman then got behind the wheel as he "felt obligated" and that "he had a duty" to drive, despite never holding more than a learner's permit which had expired in 2022.
He said Jackman fell asleep while travelling at around 90 kilometres per hour.
"He woke up and he tried to steer the car onto the road," Mr Guidice said.
Mr Guidice said that Jackman was sorry for the pain he had caused the family of the three deceased.
He requested a pre-sentence psychological report, which the court heard could take 16 weeks.
Jackman's bail was extended with a $5,000 personal undertaking, a $2,500 surety, and conditions including reporting to police twice a week and providing urine samples.
He is due to appear before the District Court in Geraldton next February.