Kieran Loveridge, who was convicted of killing 18-year-old Thomas Kelly in a one-punch attack in Sydney in 2012, has been released from prison on parole.

The 30-year-old's release from the Broken Hill Correctional Centre comes 11 years into his 13-year-and-eight-month sentence.

Mr Kelly was on his phone during a night out in Kings Cross when a heavily intoxicated Loveridge moved out from a wall and punched him, causing the victim to stumble and hit his head on the concrete.

Loveridge fled from the scene and Mr Kelly was rushed to St Vincent's Hospital. 

He died two days later when his life support was switched off.

Loveridge assaulted four other people on the same night.

He was convicted for the manslaughter of Mr Kelly, serving 10 years and six months for the killing. 

It prompted minimum sentencing laws for one-punch incidents as well as controversial lockout laws aimed at reducing alcohol-fuelled violence.

Mr Kelly's family chose not to oppose Loveridge's release, but have since objected after hearing of recent violent outbursts in prison.

At an April parole hearing, the pair heard Loveridge had repeatedly been violent, assaulting multiple people.

In one incident, he punched Rebels bikie Matthew Rymer at Silverwater Correctional Complex in 2018.This resulted in an extra 12 months being added to his sentence.

In February of this year, Loveridge was drunk and violent towards corrections officers.

Ralph Kelly said his family was told Loveridge was reforming and regretted what he had done to their son — but believed the facts of his time in prison say otherwise.

"It's hard to believe that the state parole authority think that he won't be a risk to the community — or a low risk, as they say," he told 7.30.

"Given that he had an outburst on the 27th of February it shows that he is still the same person that he was 12 years ago."

His wife, Kathy, felt that was underselling the incident.

"[It was] not just an outburst," she said.

"He was drunk in prison and was aggravated.

"We're talking a month-and-a-half ago. And we weren't aware of that when we put the submission forward saying that we supported the parole.

Corrective Services NSW said its decision was considered.

"When deciding parole, the State Parole Authority considers whether offenders have shown a willingness and commitment to change their offending behaviour, including whether they have completed the Violent Offenders Therapeutic Program," a department spokesperson told 7.30

Loveridge will have to abide by certain restrictions upon his release.

These measures including not being able to drink alcohol, not contacting the Kelly family or co-offenders, not visiting the City of Sydney and Shoalhaven local government areas.

Loveridge also cannot visit the suburb of Neutral Bay, and must not have any contact with any bikie gangs.