Australia's High Court has agreed to hear former Vatican treasurer Cardinal George Pell's final appeal to overturn his conviction for sexually assaulting two teenage choirboys.

The appeal has been referred to a full bench of five or seven judges, with the hearing on the appeal expected in March 2020 at the earliest, a court spokesman said.

Once the Vatican's third-ranking official, Pell was jailed this year for sexually assaulting two 13-year-old choirboys at a Melbourne cathedral in the 1990s.

He is the most senior Catholic convicted of child sex abuse.

The appeal comes just over two months after the 78-year-old filed an application for leave to appeal with the court.

He lost a previous attempt to overturn the convictions in Victoria state's Court of Appeal in August, a landmark decision that saw the judges split in a 2-1 verdict.

That division - which saw two judges back the jury's verdict and the dissenting judge side with Pell - is at the forefront of his latest bid to overturn the convictions.

The long-running case has pitted Pell against a former choirboy now in his 30s, who two of the appeal judges found to be "very compelling" and someone who "was clearly not a liar, was not a fantasist and was a witness of truth".

The third judge, however, found the victim's account "contained discrepancies" and there was a "significant possibility" Pell did not commit the offences.

Pell's legal team argued in their written submission to the High Court that the majority judges applied an "erroneous judicial method" in upholding the jury's verdict that reversed the onus of proof onto him, an argument roundly rejected by prosecutors.

Pell and his supporters have staunchly maintained he did not commit the crimes, which came to light after one of the victims went to police when the other died of a drug overdose in 2014.

During Pell's trial under a court-ordered veil of secrecy, the Vatican gradually removed him from top Church bodies with little explanation.

Shortly after his conviction, Pell was removed from the so-called C9 Council of Cardinals that are effectively the Pope's cabinet and inner circle of advisers.

The Vatican says it will avoid launching an investigation into his conduct until after all legal avenues are exhausted.