The original sentence of five years and two months imposed on Loveridge for a string of unprovoked assaults on five young men in Kings Cross was quashed by an appeal court on the grounds it was "manifestly inadequate" and failed to incorporate the need to deter others from engaging in alcohol-fuelled violence.

Following a furious response from sections of the community, particularly Mr Kelly's parents who launched a vocal campaign for tougher penalties for one-punch manslaughter cases and alcohol-related violence more generally, the Director of Public Prosecutions appealed against the sentence handed down by Justice Stephen Campbell in the NSW Supreme Court in November last year.

The Court of Criminal Appeal agreed and in July, Loveridge's total sentence was increased to 13 years and eight months with a non-parole period of 10 years and two months.

Loveridge's lawyers have now filed an application for special leave to appeal in the High Court on a number of grounds, including the appeal court's failure to properly take into account that he was an Aboriginal offender from a deprived background.

Loveridge's parents split when he was young and his father is a convicted criminal who has served time and jail and has a history of drug and alcohol abuse.

Loveridge's barrister and immediate past president of the NSW Bar Association, Phillip Boulten SC, says the appeal court was also wrong to overrule Justice Campbell's finding that Loveridge was remorseful, unlikely to reoffend and had good prospects of rehabilitation.

The three-judge appeal panel also failed to consider how the enormous publicity attached to the case would deter Loveridge from committing further crimes of violence, Mr Boulten said in documents filed with the High Court.

Further, the application suggests Loveridge was made an example of by the appeal court when it ruled his sentence needed to be increased because "violence on the streets, especially by young men under the influence of alcohol, is all too common".

Mr Boulten argues there was in fact not a prevalence of one-punch deaths by young offenders within the community that called for a message of deterrence to be sent by the judiciary.

The DPP is yet to file its submissions. The application for special leave to appeal is likely to be heard later this year or early next year.

Ralph Kelly, Thomas' father, told The Sun-Herald the family was "gobsmacked" by the High Court challenge but declined to comment further as the case would be returning to court.

Mr Kelly, 18, was on his first night out in Kings Cross when he was punched by Loveridge. He fell, hitting the pavement and suffered catastrophic head injuries. He later died in hospital.

Following his death and that of another teenager, Daniel Christie, in similar circumstances in January this year, the NSW Government introduced legislation prescribing eight-year mandatory minimum sentences for alcohol or drug-fuelled, one-punch manslaughter cases.