Disgraced Australian Cardinal George Pell has been sentenced to six years in prison for sexually abusing two choirboys, in what the judge lambasted as a "brazen" attack and "grave" abuse of power.

Pell, who has maintained his innocence and plans to appeal, appeared in a Melbourne court after being convicted on five offences, including oral rape and molestation of the boys in 1996-1997.

The 77-year old, wearing a black shirt but without his usual white clerical collar, sat impassively, hands interlaced on his lap as Judge Peter Kidd graphically described his "breathtakingly arrogant" attacks.

You "may not live to be released from prison" Judge Kidd acknowledged, as he accused the former Vatican number three of "appalling offending" and a "brazen and forceful sexual attack on the two victims".

He was ordered to sign the sex offender register and stood as the judge set the minimum sentence Pell would have to serve at three years and eight months, due to Pell's "otherwise blameless life".

The cardinal faced a maximum 50 years in prison for the five charges.

Pell was found guilty of cornering the two boys, who were aged 13 at the time and 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 himself 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 Judge 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 fondled him had a "profound impact" on the life of his victims.

One of the victims died of an accidental heroin overdose in 2014 having never disclosed the abuse he suffered at the hands of Pell.

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"A small amount of justice has been done today. I don't think six years is long enough," said a victims' advocate outside the court who gave her name as Rhonda.

Pell is the most senior member of the clergy to be convicted of historical child sex abuse.

Until recently he ran the Vatican's finances and helped elect popes.

With global attention on historic abuse within the Catholic church, Judge Kidd however 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.

 People watch on as Chief Judge Peter Kidd hands down his sentence outside Melbourne County Court

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 ten character references for the Cardinal, including from former prime minister John Howard and Australian National University vice chancellor Greg Craven.

The lawyer told Judge Kidd that behind bars, Pell would be considered a "lightning rod" for the sins of the Catholic Church.

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

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.