Jomen Blanket, a Noongar and Torres Strait Islander man, was aged 30 when he was found dead in his cell at the privately operated Acacia Prison in June 2019.
The father of three had harmed himself and threatened to take his life multiple times in the preceding months.
The inquest began on Tuesday and is scheduled to hear evidence across two days from prison operator Serco, WA Police and the state justice department.
Blanket's family has expressed concern there are no plans to call expert witnesses who could weigh in on whether he received appropriate treatment and care.
But an application to have the hearing adjourned so more evidence could be gathered was rejected on Tuesday by coroner Philip Urquhart.
The inquest heard Blanket, who was serving a 12-month sentence, had been placed under hourly observations at Acacia after self-harm incidents in early-2019.
After being refused parole in April, he told staff he intended to take his life and was temporarily transferred to a medical observation cell.
A prison psychiatrist believed Blanket was experiencing early signs of a psychotic illness but did not think he required involuntary treatment, counsel assisting Sarah Tyler said.
On the day he died, a prison officer had become concerned about Blanket's welfare and attempted to contact on-site mental health services but was unable to reach them because most staff were attending a function.
Arrangements were made later that morning to move Blanket to a medical observation cell but he died before the transfer could take place.
WA's justice department last month reviewed the death and found his supervision and care was in line with policies and procedures.
Karen Blanket believes prison officials failed to take seriously concerns about her son's mental health after he told her during a phone call that he planned to harm himself.
"They said 'he's alright, he's well looked after, there's nothing to worry about'," she told AAP.
"He was in a care unit where it's meant to be 24-hour care. They didn't do their job."
Ms Tyler said Acacia Prison had no record of the conversation between Blanket and his mother.
The family have described him as being devoted to his two sons, now aged nine and five, and six-year-old daughter.
"His children miss him dearly," Karen Blanket said.
"All we want is answers."
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