Benjamin Lightbody was hit in the side of the head with a pool ball while standing in the yard at Mt Eden jail.
The assault shattered his skull and gave him a serious brain injury.
Now CCTV footage of the assault has been released, showing the former inmate lying on the ground bleeding for several minutes while nobody - including guards - coming to his aid.
Lightbody fought for four years to get the CCTV footage, and has given it to the media to highlight what happened to him. He plans to use the video to sue Corrections for failing to keep him safe.
In 2013, Lightbody was on remand in the Serco-run prison. He was waiting to use gym equipment when he was hit in the head with a pool ball by another inmate and knocked out.
The CCTV footage shows no guards or inmates came to help him as he lay still in the yard for several minutes.
Eventually he wakes up and tries to stand. Minutes pass before he manages to get to his feet and stumbles off camera to his cell.
Lightbody had suffered a serious brain injury, but he lay in his cell for nearly two hours before a prisoner alerted a guard.
A Corrections investigation discovered that after the guard was told about the assault, he made himself a hot drink and had something to eat.
It took 32 minutes before guards called an ambulance.
Lightbody has no memory of the aftermath of the assault and only recalls waking up in hospital.
He is still suffering the results of the injury and is due for more operations on his skull. He told the Herald he struggles to sleep and eat, often vomits, and has developed a drinking problem.
"I get extremely tired and fatigued, I get the sweats, I shake, I get seizures. I wake up in the morning not wanting to face another day, not wanting to get out of bed in the morning."
He has partial paralysis on his right side. He also says he has post-traumatic stress disorder and has become reclusive.
"I didn't see the guy who hit me, so now when I'm out and about and there's people outside my vision on the side of the injury I get a bit wary," he said.
An investigation after the attack found the prison's wing was unsupervised at the time, and Lightbody lay unconscious for almost seven minutes without a guard noticing.
The report said areas of the prison were "short-staffed and under-supervised" and that there were too few staff to keep prisoners safe.
After a prisoner told a guard about the assault, the guard went to Lightbody's cell - but then "the officer returned to the staff base, made himself a drink and sat down for something to eat", the report said.
Guards waited 32 minutes before calling an ambulance, which the investigation found was an "excessive and unacceptable" delay.
"The seriousness of this incident cannot be overstated," it said, adding that if the prisoner had not raised the alarm "there was the potential for a significantly more serious outcome".
The investigation recommended a review of staff levels and processes at the prison.
Corrections initially refused to give Lightbody the footage on the grounds it would breach other prisoners' privacy and show the locations of CCTV cameras in the prison.
But the Privacy Commissioner eventually ruled Corrections was wrong to not release the footage. It also found someone had deleted or lost some of the footage.
The Commissioner has referred the complaint to the Director of Human Rights Proceedings.
Northern region commissioner Jeanette Burns told Fairfax that Corrections had offered to meet Lightbody. She said no compensation claim had been filed.