The offender, known under the pseudonym Rohan, was sentenced to more than 11 years in prison in 2021, after being found guilty by a County Court jury of 11 drug and sex offences.
Rohan and two co-offenders were accused of picking up two girls, aged 11 and 12, supplying them with drugs and alcohol, and then sexually assaulting them.
Prosecutors argued the men had reached an agreement to commit the offences and all three were guilty of all charges, irrespective of who carried out each act.
Rohan successfully challenged his convictions for two of the drug offences and four of the sex offences in Victoria's Court of Appeal.
The appeal court found Rohan suffered a "substantial miscarriage of justice" as the prosecution did not prove, and the jury did not consider, that he knew the girls were underage at the time of the offending.
Rohan was re-sentenced to eight years and six months in prison, with a non-parole period of six years.
However, the High Court allowed an appeal by crown prosecutors on Wednesday and ordered Rohan be sentenced for a third time.
Chief Justice Stephen Gageler and Justices Michelle Gordon, James Edelman, Jacqueline Gleeson and Jayne Jagot rejected the appeal court's decision, finding knowledge of age was not an element of any of the offences.Â
"Therefore it was not necessary for the prosecution to prove that the respondent knew the ages of the complainants at the time he entered into the agreement to commit the offences," the justices said, in a judgment summary.
Rohan will be re-sentenced by Victoria's Court of Appeal at a later date.
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