Matt James Nolan, 30, pleaded guilty to grievous bodily harm over the attack in July 2017 at the north Brisbane home of Sigourney Coles.

Ms Coles had a barbecue which Nolan attended and stayed the night before leaving at about 8am the next day, the Brisbane District Court was told.

He returned later that morning when Ms Coles was asleep in bed and allegedly used a jerry can found in the home to pour petrol around her room, set her alight and leave.

He was arrested in hospital later that day after having a mental health episode that required sedation and tested positive for methamphetamine, indicating use in the previous three to four days, the court heard.

Ms Coles required a skin graft and has been left with scars after suffering burns to her arms, hands, chest, neck and lip.

Nolan's family cried in the courtroom as the defence recounted their attempts to get him help for his schizophrenia in the lead-up to the attack.

"Those requests weren't heeded by authorities," barrister Joseph Briggs said.

While he knowingly took methamphetamines, Mr Briggs said Nolan believed it could help manage symptoms of his mental illness.

"He thought he could alleviate the hallucinations by the use of methamphetamines," he said.

He said the attack didn't appear to be planned because Nolan found the petrol at the home and his robotic behaviour was "consistent of a mind governed by profound psychoses".

Ms Coles has also been "extraordinarily generous" in her forgiveness and does not want Nolan to spend more time in jail, the court heard.

Mr Briggs also noted a course of treatment since the alleged attack had been "remarkably successful".

Nolan's bail was extended and the sentence is expected to be delivered on Monday.

Australian Associated Press