The 77-year-old cardinal appeared drained and slimmer after two weeks in custody as he stepped into the dock for his County Court sentence on Wednesday.

He sat emotionless and unflinching, minus his clerical collar for what is believed to be the first time in public since his 1966 ordination.

Chief Judge Peter Kidd ordered Pell to serve up to six years in prison for his "brazen" sexual crimes against two 13-year-old boys at St Patrick's Cathedral in Melbourne in 1996.

Pell has congestive heart failure and hypertension and the sentence reflects a "substantial portion" of his remaining life expectancy, Judge Kidd remarked in front of a packed court gallery and global broadcast audience.

"I am conscious that a term of imprisonment ... carries with it a real, as distinct from theoretical, possibility that you may not live to be released from prison," he said.

He will be 80 at his earliest opportunity for release on parole.

The sentence took into account the brazenness of Pell's offending and its lasting impact.

"It is hard for me, for the time being, to take comfort in this outcome," the surviving victim, now in his 30s, said through his lawyer.

"I appreciate that the court has acknowledged what was inflicted upon me as a child."

Six years wasn't long enough for the father of the other boy, who died in 2014.

"Our client is disappointed with the short sentencing and has expressed sadness over what he believes is inadequate for the crime," his lawyer said.

As 13-year-old choristers, the boys were the least powerful and most subordinate in the cathedral and expected to show reverence in Pell's presence, Judge Kidd said.

"The full weight of your authority and position of power must have been very obvious to your victims, and to you," he said.

Pell hadn't delivered threats to secure the boys' silence, clearly feeling he didn't need to, the judge said.

"In my view, your conduct was permeated by staggering arrogance."

The first incident in the priest's sacristy in late 1996 was sexually graphic and both victims were distressed and crying, Judge Kidd said.

"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," he said.

The second act against one boy a month later, though "brief and spontaneous", was not an "isolated lapse" because he'd had time to reflect, the judge added.

"Despite this, you still indecently acted against (the boy), and did so with what I consider to be a degree of physical aggression and venom."

Pell was until late February the Vatican treasurer and is the most senior member of the Catholic Church to be jailed for child sexual abuse.

Character references from 10 of Pell's supporters, including former Australian prime minister John Howard, spoke of a man who dedicated his life to service, and particularly to vulnerable community members.

"Self-evidently you have experienced an exceptional career with the Catholic Church. You are clearly an intelligent and hard-working man," Judge Kidd said.

He determined Pell, who will be a registered sex offender for life, was not a risk of re-offending.

Pell continues to maintain his innocence and will in June seek to appeal his conviction for one charge of sexual penetration of a child and four of indecent acts with a child.

Australian Associated Press