The Pope said in July that he would canonise his two predecessors, after approving a second miracle attributed to John Paul.
Polish John Paul, the first non-Italian pope for more than 400 years, led the Catholic Church from 1978-2005.
Pope John was pontiff from 1958-1963, calling the Second Vatican Council that transformed the Church.
The decision to canonise the two at the same time appears designed to unify Catholics, correspondents say.
John Paul II is a favourite of conservative Catholics, while John XXIII is widely admired by the Church’s progressive wing.
John Paul stood out for his media-friendly, globetrotting style. He was a fierce critic of both communism and what he saw as the excesses of capitalism.
John is remembered for introducing the vernacular to replace Latin in church masses and for creating warmer ties between the Catholic Church and the Jewish faith.
He has a big following in Italy, where he is known as Il Papa Buono, the good pope.
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