Cardinal Pell will be registered as a sex offender, with a reporting period for life.
County Court Chief Judge Peter Kidd will sentence Pell in a hearing which began at midday.
Pell abused the 13-year-old choir boys in a Melbourne cathedral in 1996, a jury ruled last year.
Pell has maintained his innocence throughout and has filed an appeal on three grounds, set to be heard in June.
For two decades, George Pell was the dominant figure in the Catholic Church in Australia - a boy from a gold mining town whose ambition, intellect and knack for befriending influential people propelled him to become the third-most senior official in the Vatican.
He was orally raped by Pell in the priest's sacristy after a Sunday mass in December 1996, forced to watch as Pell molested his 13-year-old friend, and then molested again by Pell a month later. "Everything is overshadowed by the forthcoming appeal", he said in a statement read by his lawyer.
Pell will be eligible for parole after three years and eight months.
The Royal Commission found that seven percent of Australian priests had been accused of sexual abuse between 1950 and 2011, the average age of their victims was 11 for girls and 12 for boys.
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"I think really, the point is, under the systems that work at the moment and the sentencing of other convicted paedophiles, it's a tough sentence", Neil Mitchell 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".
In sentencing Pell, Kidd dismissed mental impairment as a factor in Pell's decision to offend.
"None of it seems to fit the crime", she said.
Pell did not take the stand in his defense, 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".
"I find beyond reasonable doubt that, on the specific facts of your case, there was a clear relationship of trust with the victims, and you breached that trust and abused your position to facilitate this offending", the judge said.
"You are not to be made a scapegoat", he said.
The judge said there was a "real" possibility that Pell may not live to be released from prison, and that he had considered the cleric's age and health in sentencing.
"Hopefully this sentence can herald fundamental change to the Church and other institutions, starting with accountable, responsible and transparent leadership, hierarchy and culture".
Another conservative former prime minister, John Howard, provided a written character reference for Pell in court after his conviction, saying he had known Pell for 30 years.