The man found guilty of killing Sydney teenager Daniel Christie in a one-punch attack at Kings Cross in 2013 has been sentenced to a maximum of 10 years in jail.

Shaun McNeil, 27, was found not guilty of murder but guilty of manslaughter in June and will be eligible for parole in 2021.

Shaun McNeil, 27, was found not guilty of murder but guilty of manslaughter in June and will be eligible for parole in 2021. ( ABC TV )

Supreme Court Judge Justice Robert Allan Hulme said Mc Neil had violently punished an innocent young man.

"Daniel Christie was no match for him," Justice Hulme said.

"The offender struck him unnecessarily, without warning. It was a ferocious blow delivered by a powerfully built man."

Justice Hulme also said McNeil's actions were cowardly.

"It is not as if violence is out of character for the offender," he added.

Daniel's Mother Maureen Christie spoke publicly for the first time outside court.

"It's not acceptable for anyone to have to experience the loss of a loved one as a victim of crime," Ms Christie said.

"What happened to Daniel is both brutal, senseless and unjustified. Daniel was the most loving person. He was kind, generous, gentle and respectful. He was entitled to so much more life.

"At just 18 our beautiful Daniel lost everybody and everything.

Daniel Christie died 11 days after he was punched by Shaun McNeil on New Years Eve in 2013. ( Supplied )

"There is not a sentence that any court could give that would equate to my family's loss."

Daniel's father Michael Christie also spoke outside court, saying he hoped the offender would rehabilitate.

"We as a family stand here today incomplete because of course Daniel is not with us," Mr Christie said on Thursday.

"But as Daniel said, 'If change is to be it's up to me'; and that was his mantra and how he lived his life.

"I would just hope the offender has as much courage as Daniel does to do the same thing so that his reoffending in the future doesn't become even more habitual than what it has been in the past."

He encouraged young people to come forward and talk about the dangers of alcohol.

"It is a drug. Full stop. And it can ruin people's lives as we've seen."

McNeil was arrested on New Year's Eve 2013 shortly after his attack on the 18-year-old, who was out celebrating with his brother Peter.

A police video, which was shown to the court and released after the verdict, shows McNeil telling a police officer a "scuffle" broke out after a conversation with a group of people in the street.

The jury was told McNeil got into a fight with a separate group of three teenagers who had tried to sell him the drug ecstasy a short time earlier.

Sorry, this video has expired Shaun McNeil speaks to police after the assault

In sentencing, the judge said that as a result of the remorse shown by McNeil in his police interview immediately after the attack "I am prepared to find the offender is probably sorry".

"I cannot conclude that his prospects for rehabilitation are good, but I do accept they are reasonable."

But the judge said he could not conclude that McNeil would not reoffend.

Grief is all consuming: Christie's father

Last week Michael Christie delivered a devastating victim impact statement to the court.

He said his grief had become "all consuming" and his son's death had led to "pain, torment and [an] overwhelming feeling of loss".

Mr Christie said he suffered from depression and "had thoughts of taking [his] own life".

"Breathing is almost impossible. Sometimes you wish you would just stop breathing," he said.

Shaun McNeil's mother and step-father, Sharon and Liam McCormack, leave court. ( Fairfax Media: Janie Barrett )

Mr Christie told the court that Daniel's brother Peter must now live his life with the images of the night his brother was attacked, "the sound of his skull cracking ... the smell of blood oozing from his wounds".

Daniel died in hospital 11 days after the attack.

Mr Christie said it was "the most mentally gruelling 11 days imaginable of anyone's life, the hope giving way to acceptance of the finality of death".

He said the moment he turned off the life support machine "can only be described as haunting".

McNeil's trial jury was told that, before he assaulted Daniel, McNeil had been in a fight with a group of teenagers who tried to sell him ecstasy.

The 27-year-old punched one of the teenagers, then kicked him while he was on the ground.

Daniel was heard saying: "What's going on? What are you hitting a kid for?"

McNeil responded: "I'm an MMA fighter."

He then punched Daniel, who fell backwards and hit his head on the ground.

McNeil told police he mistook Daniel as being part of the group of teenagers who had offered him drugs.

Daniel's death triggered intense debate over alcohol-fuelled violence in Sydney.

He fell just metres from where Thomas Kelly, 18, was fatally punched by Kieran Loveridge on June 7, 2012.

The debate led to the introduction of new laws including early lockouts, a freeze on new liquor licenses in the city and a 10:00pm closing time for bottle shops.