Cardinal George Pell has taken his legal fight to overturn his child sex abuse convictions to the High Court of Australia.

Key points: Pell's legal team has lodged an application for leave to appeal in Australia's highest court

Pell's legal team has lodged an application for leave to appeal in Australia's highest court It came one day before the deadline for the application to be submitted

It came one day before the deadline for the application to be submitted The highest-ranked Catholic official to be found guilty of child abuse has always maintained his innocence

A 12-page application seeking leave to appeal has been lodged, following the Victorian Court of Appeal's dismissal of Pell's appeal in August.

The 78-year-old former adviser to the Pope is currently serving a maximum six-year prison sentence for the sexual abuse of two former choirboys at St Patrick's Cathedral while he was the Catholic archbishop of Melbourne in the 1990s.

Pell has to serve three years and eight months in jail before being eligible for parole.

Pell's legal team had 28 days to lodge leave to appeal in the High Court after the appeal judges dismissed his case on August 21.

The Cardinal's legal team had been thoroughly examining the court's judgment after a 2-1 split decision was handed down by the three judges.

The two proposed grounds for appeal focus on that majority decision to dismiss Pell's case.

"The majority erred by finding that their belief in the complainant required the applicant to establish that the offending was impossible," the application states.

The proposed second ground is "the majority erred in their conclusion that the verdicts were not unreasonable".

Pell's legal team is seeking for his convictions to be quashed.

If leave to appeal is granted it will be his final opportunity to challenge the convictions, but there is no guarantee the High Court will agree to hear the appeal.

The court can decide to grant leave to appear from the written application, or may request a short hearing — which is unlikely to be heard until next year unless the case is expedited.

Appeal judges split on victim's testimony

The High Court is likely Pell's final legal avenue to make a bid for freedom. ( ABC News )

Pell is the highest-ranking Catholic official to be found guilty of child abuse.

He has always maintained his innocence.

His lawyers had submitted that the offending could not have occurred in the time frame given, in a busy cathedral after solemn mass and given the then-archbishop was always accompanied.

It was the testimony of the surviving victim that became a sticking point between the Court of Appeal judges.

Chief Justice Anne Ferguson and Justice Chris Maxwell dismissed the appeal ground that the jury's verdict was "unreasonable", finding instead the complainant was a compelling witness who came across as truthful.

"The complainant was a very compelling witness, was clearly not a liar, was not a fantasist and was a witness of truth," Chief Justice Ferguson said.

However the third judge, Justice Mark Weinberg, said he was "quite unconvinced" by the victim's evidence, stating it "contained discrepancies, displayed inadequacies" and it was possible that some of what he said was concocted.

The judges unanimously dismissed two other grounds of appeal, which argued there were errors in the way the trial was run.

The Archbishop of Sydney, Anthony Fisher, said last month the split decision was "consistent with the differing views of the juries in the first and second trials, as well as the divided opinion amongst legal commentators and the general public".

Pell was found guilty by a jury of abusing two boys at St Patrick's Cathedral. ( ABC News: Danielle Bonica )

In order for the High Court to grant leave to appeal they must be satisfied an error in law has occurred.

If an appeal hearing is granted it is unlikely to be heard before next year.

The Vatican's decision on whether the Cardinal will be laicised, or removed from the priesthood, is expected to wait until he has exhausted all avenues of appeal.

Editor's note: On Tuesday April 7, 2020, the High Court in a unanimous decision upheld Cardinal Pell's appeal and quashed his convictions on all five charges.