Disgraced Australian Cardinal George Pell was on Wednesday sentenced to six years in prison for the "brazen" sexual abuse of two choirboys, in what the judge lambasted as a "grave" abuse of power.

The former Vatican number three -- who managed church finances and helped elect two popes -- was sentenced in a Melbourne court on five counts, including oral rape and molestation of the boys in 1996-1997.

Judge Peter Kidd, his remarks broadcast live on television, said the 77-year-old was guilty of "appalling offending" and "breathtakingly arrogant" attacks that took advantage of his position of authority over the boys, then aged 13.

Kidd said the cardinal, with his "significant history of cardiac problems," would be eligible for parole in late 2022, but acknowledged he "may not live to be released from prison."

Wearing a black shirt without his usual white clerical collar, Pell sat largely impassively, hands interlaced on his lap, as Kidd graphically described his "brazen and forceful sexual attack on the two victims."

He was ordered to sign the sex offenders' register and stood as a sentence well short of the maximum 50 years was set by Kidd, who cited Pell's "otherwise blameless life."

"You have effectively reformed," Kidd said, noting the 22 years since the abuse. "You are not a risk to the community."

The cardinal, a household name in Australia with friends that include prime ministers and business magnates, maintains his innocence and will appeal.

The prospect of further legal proceedings and the relatively short sentence tempered victims' response to the news.

"There is no rest for me," the victim named only as "J" said in a statement, read by his lawyer Vivian Waller.

"I appreciate that the court has acknowledged what was inflicted upon me as a child," he said. "Everything is overshadowed by the forthcoming appeal."

The father of the other victim, who died of a drug overdose in 2014, said through his lawyer that the length of Pell's sentence was "disappointing".

Pell was found guilty of cornering the two boys, who were on scholarships to the prestigious St Kevin's College, in the sacristy after Sunday mass at St Patrick's Cathedral in December 1996, when he was archbishop of Melbourne.

The boys had "nicked off" from the rest of the choral procession and were taking swigs of sacramental wine before the cardinal found them, opened his robe, exposed his penis and sexually assaulted them.

"There is an added layer of degradation and humiliation that each of your victims must have felt in knowing that their abuse had been witnessed by the other," said Kidd.

The judge added that the attack, and another two months later in 1997, when he forced one of the boys up against the wall of a corridor and grabbed his genitals, had a "profound impact" on the lives of his victims.

'Church not on trial'

Pell is the most senior member of the clergy to be convicted of historical child sex abuse and his future inside the church is now far from clear.

But with global attention on historic abuse within the Catholic church, Kidd stressed that it was Pell rather than the Vatican that was on trial.

He began the hearing, which was broadcast live, by stating that Pell was "entitled to the balanced and steady hand of justice" and lamenting "lynch mob mentality" among some of the public.

"You are not to be made a scapegoat," he said.

However, tensions ran high outside the court, with one self-declared abuse survivor breaking down in tears as he listened to a broadcast of the hearing, and another assailing Pell's departing lawyer with cries of "dirty money."

Pell did not take the stand in his defence, but in a video of his police interview in Rome in 2016 he called the allegations against him "deranged falsehood" and "a load of absolute and disgraceful rubbish."

During a pre-sentencing hearing in February, Pell's lawyers submitted 10 character references for the Cardinal -- including from former Prime Minister John Howard and Australian National University vice-chancellor Greg Craven.

Pell's appeal has been slated for a hearing on June 5 and 6.

His legal team is appealing on the grounds that the jury's verdict was unreasonable, that Pell was not arraigned in the presence of the jury panel, and that the defence was prevented from showing the jury a visual presentation -- described as similar to a "Pac Man" video game -- depicting the movement of priests in the cathedral on the day of the choirboys' abuse.

Pell's conviction -- which has been criticised by prominent commentators and friends of the cardinal -- came about as a result of a retrial after the first jury was unable to reach a verdict in September.

Media outlets were unable to report the guilty verdict until last month, when a suppression order was lifted after a second trial mounted against Pell -- involving allegations stemming from a Ballarat swimming pool in the 1970s -- was dropped.

One complainant in that case, who alleged he was molested by Pell, has launched civil proceedings against him, as well as against the State of Victoria, the Sisters of Nazareth and Child and Family Services Ballarat.