The ex-Vatican treasurer abused two boys in 1996, a jury found in December.
Pell’s bail was revoked on Wednesday, placing him in custody for the first time. He will be sentenced on 13 March.
The cardinal is the most senior Catholic figure ever convicted of sexual abuse. He maintains he is innocent and has lodged an appeal.
A jury unanimously convicted Pell of one charge of sexually penetrating a child under 16, and four counts of committing an indecent act on a child under 16.
The verdict and details of the case had been kept secret until Tuesday due to legal reasons.
Each charge carries a maximum sentence of 10 years in jail, a court heard on Wednesday.
Pell’s conviction has rocked the Catholic Church. He was considered one of the Pope’s closest advisers and spent five years overseeing the Vatican’s finances.
On Tuesday, the Vatican confirmed that Pell was prohibited from public ministry, and banned from having contact with minors. He has to abide by these rules until any appeal is over.
What has he been convicted of?
Pell was archbishop of Melbourne when he abused two 13-year-old boys in a cathedral following a mass, the County Court of Victoria heard last year.
After telling them they were in trouble for drinking communion wine, Pell forced each boy into indecent acts, prosecutors said. He abused one of the boys again in 1997.
What happened on Wednesday?
In a preliminary sentencing hearing, Pell’s lawyer, Robert Richter QC, described it as “no more than a plain, vanilla sexual penetration case”.
He submitted 10 character references for the cardinal, including from former Australian Prime Minister John Howard.
However, prosecutors argued that Pell’s “serious offending” warranted significant jail time.
Judge Peter Kidd said the abuse was “callous” and “brazen”, adding: “It did involve a breach of trust and a degree of impunity. How else did he think he was going to get away with it?”
He revoked Pell’s bail following a lengthy hearing.
First night in custody
Hywel Griffith, BBC News Australia correspondent
George Pell bowed towards the judge and leaned on his walking stick, before officers took him down from the courtroom and into custody.
Earlier, he’d arrived to face a crowd of angry campaigners waving placards – many had come to see the moment he lost his liberty.
Though an appeal looms, Pell will return to court in two weeks to learn his sentence.
Who is George Pell?
The Australian cleric rose in prominence as a strong supporter of traditional Catholic values, often taking conservative views and advocating for priestly celibacy.
He was summoned to Rome in 2014 to clean up the Vatican’s finances, and was often described as the Church’s third-ranked official.
But his career has been dogged first by claims that he covered up child sexual abuse by priests, and then later that he was himself an abuser.
Pell was demoted from the Pope’s inner circle in December. His term as Vatican treasurer expired on Sunday.
What is the wider picture?
The sexual abuse of children was rarely discussed in public before the 1970s, and it was not until the 1980s that the first cases of molestation by priests came to light, in the US and Canada.
In the decades since, evidence of widespread abuse has emerged globally. In Australia, an inquiry heard that 7% of the nation’s Catholic priests had abused children.
Pope Francis has established a committee to tackle sexual abuses. In recent days, he has promised concrete action, calling clergy guilty of abuse “tools of Satan”.
But critics say he could do more to combat paedophiles and those who conceal abuse.