The ex-Vatican treasurer, 78, was the most senior Catholic figure ever jailed for such crimes.
In 2018, a jury found he abused two boys in Melbourne in the 1990s.
But the High Court of Australia quashed that verdict on Tuesday, bringing an immediate end to Cardinal Pell's six-year jail sentence.
The Australian cleric had maintained his innocence since he was charged by police in June 2017.
His case rocked the Catholic Church, where he had been one of the Pope's most senior advisers.