The three possible outcomes of George Pell's appeal

Disgraced Cardinal George Pell will learn whether he will walk free from prison or remain behind bars when Victoria's Court of Appeal hands down its decision this morning.

Pell was convicted in December of five charges over the rape of one 13-year-old choirboy and sexual assault of another at St Patrick's Cathedral in Melbourne in 1996.

Three justices heard Pell's appeal over two days in June.

The Court of Appeal will rule today if Pell walks free, faces a retrial or is sent back to prison to serve out his six-year jail term. Pell is not appealing the length of the jail sentence.

Bret Walker SC argued three grounds to secure Pell's release or a retrial, including that the verdicts were "unsafe and unsatisfactory".

George Pell could walk free on Wednesday as his appeal is decided by the Court of Appeal. Source: AAP

If the judges accept that position, Pell will walk free on Wednesday.

He was sentenced in March to six years in prison, to serve three years and eight months before becoming eligible for parole.

Two other appeal grounds could secure Pell a retrial, unless the court determines forcing Pell to stand trial a third time would be unjust. In that case Pell would also walk free.

Abuse not physically possible, Pell’s defence argues

Evidence from prosecution witnesses showed Pell greeted parishioners after mass, when the offending was said to have occurred, so it was not possible for him to have committed the "atrocious" crime, Mr Walker said in the appeal.

"If (Pell) was at the western door, then the law of physics tells us this is literally, logically impossible for the offending to have occurred according to the complainant's account, and there is no other account," Mr Walker said.

Cardinal George Pell leaves the Supreme Court of Victoria in June. Source: AAP

The other of Pell's victims died in 2014, aged 31, from a drug overdose.

The boy's father, who is suing the priest and the Catholic Church, claiming his son's death was linked to his sexual abuse, confirmed on Tuesday he would continue his fight for compensation whether or not Pell was released from jail.

Prosecutor Chris Boyce QC told the appeal justices that the surviving boy, now aged in his 30s, had stood up to "one of the great old-style cross-examinations" with calm, reliable and credible testimony in last year's trial.

"He was a witness of truth," Mr Boyce said.

Chief Justice Ann Ferguson will read a summary of the court's judgment on Wednesday morning, before publishing the full reasons for the decision.

Justice Ferguson's summary will be live streamed.

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