Serco will end its management of Mt Eden Prison today after four years riddled with allegations of fight clubs, poor supervision and understaffing.
The government handed over management of the prison to the UK-based company in 2011 but took it back in 2015 after the allegations were made public.
Since then Serco has only been involved in a labour supply agreement, which finishes today, leaving Corrections back in control.
At the time government handed over management, it said it was confident the company would succeed.
After cases of fight clubs made headlines, a Chief Inspector's report found organised fighting was happening at least once a week.
A staff member had also taken part in sparring.
The report concluded there was a lack of supervision and staff were a primary source of contraband.
Last year, Corrections chief executive Ray Smith described Serco's management as "willy-nilly" with failures on a large scale.
Labour's Corrections spokesperson Kelvin Davis said the problems were insurmountable and Serco had to go.
"It was a total disaster from start to finish. It's a pity it took so long for all the problems to emerge," he said.
"Once the fight club videos started coming out it became obvious that the prison was out of control and then the stories just started flooding in to me."
The government should never have given Serco the contract, Mr Davis said.
"I just don't think the privatisation of prisons works, because if they're successful then people won't go back to prison which means they won't make money. So [if there's] any organisation that actually has a vested interest in being unsuccessful it'd be private operators of prisons.
"The best thing I can say to them is haere rā."
Since taking over in 2015, Corrections has employed a new prison director and leadership, reconfigured the prison units and added 50 more staff.
Northern regional commissioner Jeanette Burns said the prison was now running smoothly.
"We've brought it back up to a Corrections standard essentially, around numbers of staff, systems and process, general cleanliness of the prison. All those things that allow you to have good order and control in a prison," she said.
"Prisoners are feeling safer and they've got more routine, they've got more activities and whilst that doesn't stop some, to them being discontented that's just part of prison life."
Serious assaults between prisoners had dropped by about 55 percent, from 11 a year to five, since Corrections stepped in.
However, there had been a rise in less serious assaults between prisoners and staff.
That was down to enforcing a zero-violence policy which meant greater vigilance and reporting of violence, Ms Burns said.
"There's absolutely no evidence of fight clubs in that prison. There are, however, fights occurring most days in that particular prison between individual prisoners.
"What we do is step in extremely quickly and ... stop it escalating and the prisoners have consequences."
In the lead-up to the end of the contract, 180 Serco staff have been hired by Corrections.
Serco said it had offered some staff positions at the prison it runs in Wiri, as required under its employment agreement.
"Since the step-in, we have worked closely with the [Corrections] Department and our employees at [Mt Eden] managing the needs of staff and the facility," Serco Asia Pacific chief executive Mark Irwin said in a statement.
Upon the release of the Chief Inspector's report last year Serco acknowledged it could have done better.
"In 2015 certain important areas of service delivery fell below levels which our customer, the Department of Corrections, the Minister of Corrections and the people of New Zealand had a right to expect, and for that, we are truly sorry," the company said at the time.
"Important lessons have been learnt, and we have paid the Crown $8m recognising this and the costs incurred by the Department in taking over the management of the prison in July 2015."
Corrections Minister Louise Upston said she was confident the prison was now being run well.
"I am reassured that any issues that may arise ... [at] prisons will emerge early through the changes I have made to the Corrections Inspectorate to give it more powers and ensure greater transparency.
Private prisoner operators could be held to account in future through the use of financial penalties and having their contracts ended, she said.
"There are no current opportunities for private operators in the corrections space at present but the government would not rule it out in future."