The Queensland Police Service is investigating the death in custody of 43-year-old Glen Francis at Maryborough Correctional Centre on Tuesday.
The family's spokesperson Aunty Alex Gator said the community was still in shock after hearing of his death.
"This is a death that should never have happened," she told NITV News.
"He was a member of a family, he was a member of our community.
"He was serving his time and they had a duty of care to him."
In a statement, Queensland Corrective Services (QCS) said he was found unresponsive in a single-occupancy cell after 1pm on Tuesday afternoon.
"Responding officers commenced CPR and Queensland Ambulance Service attended the centre, however he was unable to be revived," it read.
"The centre was placed into lockdown as a precautionary measure, and officers are engaging with other prisoners in the unit."
"...Our thanks go to responding officers for their professional and committed response to this challenging incident, and our condolences go to the man’s family, friends and community."
QCS said they will assist with Queensland Police with their investigation.
