An Australian court has upheld convictions against the most senior Catholic to be found guilty of child sex abuse.

George Pell, Pope Francis' former finance minister, was found guilty of molesting two 13-year-old choirboys in Melbourne's St Patrick's Cathedral in 1996 and 1997 last December.

The Victoria state Court of Appeal rejected Pell's appeal by 2-1 on Wednesday.

At the time, Pell had just become archbishop of Australia's second largest city and had set up a world-first compensation arrangement for victims of clergy sexual abuse.

His lawyers are expected to appeal the decision in the High Court, Australia's final arbiter.

Pell, 78, showed no emotion when Chief Justice Anne Ferguson read the verdict to a packed courtroom but bowed his head moments later. He wore a cleric's collar but not his cardinal's ring.

He had arrived at the court in a prison van and was handcuffed as he was led away by a guard.

Pell's lawyers had to prove to the appeals court that the jury that unanimously convicted him in December must have held a reasonable doubt about his guilt.

Prosecutors replied that the evidence of more than 20 priests, choristers, altar servers and church officials showed there were "possible hindrances" to the prosecution case, but did not preclude the jury from being satisfied beyond a reasonable doubt of Pell's guilt.

Pell's lawyers argue the events in 1996 as described in the prosecution case were "improbable and even impossible" to have happened quickly and in part of the cathedral where altar servers and priests were likely to walk in at any moment.

One of the choirboys, identified by the sentencing judge as JJ, was the key prosecution witness. His friend, identified as MR, died of a heroin overdose in 2014 at the age of 31 without ever complaining he had been abused.

The father of the dead choirboy, neither of whom can be named, attended the court hearing on Wednesday, the father lawyer's Lisa Flynn said before the hearing.

Ms Flynn said a Pell win would be "devastating" for the father, but the father would continue with a civil suit against Pell and the church regardless of the outcome.

When sentencing Pell to six years in prison in March, the trial judge accused Pell of showing "staggering arrogance" in his crimes.

Pell was ordered to serve a minimum of 3 years and 8 months before he was eligible for parole.