Once the Vatican's third-ranking official, Pell had been trying to overturn the verdicts and six-year sentence for sexually assaulting two 13-year-old choirboys at a Melbourne cathedral in the 1990s.
The high-profile case pitted the powerful 78-year-old -- who previously helped elect Popes, ran the Vatican's finances and was involved in the church's response to child sex abuse claims -- against a single surviving former choirboy.
Pell, dressed in a dark suit, occasionally bowed his head as Chief Justice Anne Ferguson dismissed his arguments and described his victim as "very compelling" and someone who "was clearly not a liar, was not a fantasist and was a witness of truth."
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The ruling prompted cheers to ripple into the courtroom from a large crowd gathered outside, and produced emotional statements from victims, their families and advocacy groups.
The now-adult victim -- who cannot be named for legal reasons -- said the "stressful" four-year legal fight had taken him "to places that, in my darkest moments, I feared I could not return from."
Dismissing vocal media critics, the man said the death of his friend, the second choirboy, from a drug overdose had prompted him to break his silence.
"After attending the funeral of my childhood friend... I felt a responsibility to come forward," he said in a statement read by his lawyer.
"I am not an advocate. You wouldn't know my name. I am not a champion for the cause of sexual abuse survivors."
A lawyer for the father of the second victim said he felt "a weight had been lifted."
"He feels that justice has been delivered today. He has a real sense of relief that George Pell is behind bars tonight," Lisa Flynn said.
Following the ruling, Pell -- who will be eligible for parole in three years and eight months -- maintained his innocence and said he was now considering a second and final appeal.
"Cardinal Pell is obviously disappointed with the decision today," said a statement issued through the church.
"His legal team will thoroughly examine the judgement in order to determine a special leave application to the High Court."
Pell's lawyers now have 28 days to consider further legal steps.
They had raised 13 objections to his convictions, casting doubt on everything from the physical possibility of Pell removing his robes to carry out the act, to the credibility of the main witness.
The case was unusual in that it relied heavily on the closed-door testimony of the sole surviving victim.
The three judges unanimously dismissed two so-called "fallback" arguments for Pell related to alleged procedural errors during his trial.
His lawyers argued they should have been allowed to show an animated reconstruction of peoples' movements in the cathedral on the days of the assaults.
They also took issue with the fact that Pell was not arraigned in the presence of the jury. The process was completed via video link so the large pool of potential jurors was able to watch.
Ferguson said that despite these complaints the judges "decided that it was open to the jury to be satisfied beyond a reasonable doubt that Cardinal Pell was guilty of the offence charged."
Following Wednesday's ruling Australian Prime Minister Scott Morrison expressed sympathy for the victims.
He said the "courts had done their job" and indicated Pell would be stripped of his Order of Australia honour.
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During Pell's trial under a court-ordered veil of secrecy, the Vatican gradually removed him from top Church bodies with little explanation.
Shortly after his conviction, Pell was removed from the so-called C9 Council of Cardinals that are effectively the Pope's cabinet and inner circle of advisers.
The Vatican dropped him as the Church's finance chief and opened its own probe into his actions after his conviction was made public in February.
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