The other apparent victim died in 2014, and was unable to testify in the proceedings. In 2001 he denied to his mother that any abuse occurred while he was a member of the choir.
Pell was convicted in 2018, in the second trial concerning the allegations. The first trial ended in a hung jury.
After the conviction, the cardinal was sentenced to six years in prison, of which he had been required to serve at least three years and eight months before being eligible to apply for parole. Pell was to be eligible for release in October 2022.
Pell, 78, has maintained his innocence. His defence has insisted that the alleged crimes would have been, under the circumstances, "simply impossible."
The conviction has divided opinion in Australia and internationally. The cardinal's defenders have contended that the sacristy abuse allegations are not possible given the high traffic after Mass and the obstructing nature of the Mass vestments.
The cardinal has been incarcerated in HM Prison Barwon, a maximum-security prison southwest of Melbourne that holds some notorious crime bosses.
The cardinal is now expected to face a canonical proceeding in Rome, overseen by the Vatican's Congregation for the Doctrine of the Faith.
Shortly after the High Court announced its decision Archbishop Mark Coleridge of Brisbane released a statement on behalf of the Australian bishops' confernece saying that the news "will be welcomed by many, including those who have believed in the Cardinal's innocence throughout this lengthy process."
But, Coleridge said, the result "does not change the Church's unwavering commitment to child safety and to a just and compassionate response to survivors and victims of sexual abuse."
"The safety of children remains supremely important not only for the bishops, but for the entire Catholic community," the archbishop said.
This story is developing and is being updated.
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