George Pell's final bid for freedom at the High Court this week will be one of the most closely watched hearings in Australian legal history.

It's one of the most high-profile and contentious High Court cases in recent memory — up there with Lindy Chamberlain.

In December 2018, when a jury found Pell guilty of sexually abusing two choirboys, many of his supporters were hopeful the convictions would be overturned on appeal.

Only one of the former choirboys gave evidence at the trial, the other died of a drug overdose in 2014.

But a majority of the three judges at the Victorian Court of Appeal backed the jury's verdict, leaving Pell to continue serving a six-year jail term.

Now it all comes down to a two-day hearing before the full bench of the High Court starting on Tuesday.

Here's a quick guide to how the case will run.

George Pell was sentenced to six years' jail in March last year for the sexual abuse of two choirboys in the 1990s. ( ABC News: Fay Plamka )

What are the grounds for Pell's appeal?

If you have time for the long version, Pell's legal team sets out its case in a 21-page written submission to the High Court.

The Crown's response is also 21 pages and there are further written submissions on the High Court website.

Essentially, Pell's lawyers argue the Victorian Court of Appeal should have ruled that the guilty verdict handed down by the jury was unsafe.

"They say the evidence at the trial means that even if you accept the complainant's testimony as seemingly credible, it's not enough to convict Pell because the other evidence creates too much doubt," Melbourne University Law School Professor Jeremy Gans said.

"The Crown say the Court of Appeal majority considered all of that and was still left without doubt that Pell was guilty."

University of Melbourne Law School Professor Jeremy Gans said the High Court had not yet agreed to hear George Pell's appeal. ( ABC: Simon Leo Brown )

Has the High Court agreed to hear the appeal?

Funnily enough the answer is no, or at least, not yet.

Despite setting a two-day hearing where the parties will argue for and against the appeal, the High Court is yet to grant what's called 'special leave to appeal'.

George Pell's child sex abuse appeal case is one of the most high-profile cases heard at the High Court in recent memory. ( ABC TV )

It may even hear all the arguments on the appeal itself before ruling if leave is granted. That's not unusual in High Court cases.

If leave is not granted, the appeal fails, and Pell must serve his time. If leave is granted, the High Court will then make a judgment on the appeal and publish its reasons.

How will the case be heard?

The case will be heard before the full bench of the High Court. That could mean five judges or seven judges — for the moment the High Court won't say how many.

The exact number will become clear later on.

The judges won't examine all the trial evidence.

This will be Director of Public Prosecutions Kerri Judd's third appearance as lead counsel in an appeal before the High Court. ( AAP: James Ross )

"The High Court will be looking at the appeal judgment and around 100 pages of trial transcript selected by the parties," Professor Gans said.

"Each side has asked for four hours to make their case, but it's up to the court how long they have.

"If the judges disagree on the special leave application or the appeal itself, the majority decision stands."

What are all the possible outcomes?

According to Professor Gans, there are five possible outcomes from Pell's High Court application:

Refuse special leave — which ends the case and leaves Pell in prison.

— which ends the case and leaves Pell in prison. Grant special leave and dismiss the appeal — which again leaves Pell in prison, but the High Court will publish more detailed reasons.

— which again leaves Pell in prison, but the High Court will publish more detailed reasons. Grant special leave and allow the appeal — that ends the case and means Pell is cleared and must be freed immediately.

— that ends the case and means Pell is cleared and must be freed immediately. Grant special leave and send the case back to the Victorian Court of Appeal — that puts the case back where it was a year ago, after Pell was sentenced.

— that puts the case back where it was a year ago, after Pell was sentenced. Do something else — for example ask Pell and the Director of Public Prosecutions (DPP) to provide more arguments or information down the track.

Could there be a result on Tuesday?

Technically, yes.

Professor Gans said it was possible the court could decide to throw out Pell's appeal after his lawyers put their case forward.

"They could just wait until Pell's counsel is finished and say, we have heard enough, he can't win, and they could dismiss his appeal then and there or deny special leave."

The High Court will begin hearing George Pell's appeal and is likely to take at least a month to make a decision. ( AAP: James Ross )

But he said it was more likely the court would reserve a decision.

"It doesn't have to decide anything this week and typically takes a few months to make a decision and write a judgment."

Is this Pell's last chance to beat his convictions?

Pretty much.

If he loses, that's the end of the appeal process. But it's still technically possible for Pell to have his convictions overturned in the future.

"The only exception is if fresh and compelling evidence of his innocence emerges down the track," Professor Gans said.

Only last year, Melbourne man Faruk Orman had a murder conviction quashed despite earlier having his application for leave to appeal rejected by the High Court.

Mr Orman was freed by the Victorian Court of Appeal after it emerged his lawyer Nicola Gobbo (aka Lawyer X) was a police informer and had helped coach the main witness. Lindy Chamberlain-Creighton was also eventually freed despite losing at the High Court.

Lindy Chamberlain-Creighton was wrongly convicted of murdering her nine-week-old baby in Uluru in a case that spanned more than 30 years. ( AAP: Xavier La Canna )

Which lawyers will argue the case?

Prisoners don't usually attend High Court cases, unless they are representing themselves. Instead Pell will be at Barwon Prison near Geelong while the case is heard.

Here's Professor Gans's take on the lawyers arguing the case:

For Pell: Bret Walker SC, probably Australia's top lawyer. He appears all the time in the High Court, and also represented Pell at his Victorian appeal last year.

Bret Walker will represent George Pell this week alongside Pell's second barrister Ruth Shann. ( AAP: Julian Smith )

With him is Ruth Shann, who was Pell's second barrister at his trials and his Victorian appeal (Robert Richter QC, Pell's main barrister at his trials, is no longer on the case).

For the DPP: Kerri Judd QC, Victoria's Director of Public Prosecutions since March 2018. This case will be her third-ever appearance as lead counsel in an appeal before the High Court, and it's the first time she's represented the prosecution in court in Pell's case.

With her is Mark Gibson QC, the prosecutor at Pell's two trials in 2018 (Chris Boyce QC, the prosecution's main barrister at the Victorian appeal, is no longer on the case).

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.