Pope Francis gave the go-ahead on Friday for John Paul II to be made saint and granted a rare exception for canonisation at the same time for John XXIII, who shares the current pontiff's reformist views and personal touch.
The announcement marked a historic day at the Vatican, which also issued an unprecedented text co-written by Francis and his living predecessor Benedict XVI in which the two popes said faith was a "common good" and called for dialogue with non-believers.
The Vatican said Francis gave his widely expected formal approval to a second miracle attributed to John Paul II (1978-2005) at a meeting with Cardinal Angelo Amato, head of the Congregation for the Causes of Saints.
The supposed miracle occurred to a woman in Costa Rica, the Vatican said, following media reports that she had been cured of a serious brain condition by praying for the late pope's intercession on the same day that he was beatified in 2011.
John Paul II (1978-2005) was hugely popular through his 27-year papacy, and helped topple Communism although he alienated many Catholics with his conservative views and was blamed for hushing up multiple scandals over paedophile priests.
At his funeral in 2005, crowds of mourners cried "Santo Subito!" -- which roughly translates as "Sainthood Now!" -- prompting the Vatican to speed up the path to sainthood, which normally begins five years after the death of the person in question.
In the case of John XXIII (1958-1963), Francis "approved the favourable votes" from the Congregation for the canonisation even though no second miracle has been found, in a break with the usual procedure.
The long road to sainthood normally requires two "confirmed" miracles, the first of which is necessary for beatification, a hurdle the Polish pope cleared just six months after his death.
That was the healing of a French nun, Sister Marie Simon-Pierre, whose recovery from Parkinson's disease after praying for the late John Paul II's intercession apparently had no medical explanation.
The announcement on John XXIII was greeted with bells ringing out in a parish church in the village of Sotto Il Monte in northern Italy where he came from.
A consistory, a meeting of cardinals, will now be held to determine the exact date for the canonisations but Vatican spokesman Federico Lombardi said they would take place "before the end of the year".
Nicknamed "The Good Pope", John XXIII made his name by calling the historic Second Vatican Council (1962-1965) which overhauled and modernised the Catholic Church's rituals and doctrines.
Francis also promises to be a reformist pope, planning an overhaul of the Vatican bureaucracy and its finances and promising a "poor Church for the poor".
The current pontiff is often compared to John XXIII for his pastoral attitude and charisma, which contrasts with the more austere and academic style of Benedict XVI.
A religious text issued by the Vatican on Friday, however, showed that behind the differences in style there was continuity between Benedict and Francis.
The encyclical was co-written by the two men -- a first in Church history -- and highlights the importance of faith in modern society, as well as restating the Vatican's opposition to gay marriage.
Faith "does not simply brighten the interior of the Church, nor does it serve solely to build an eternal city in the hereafter, it helps us build our societies," read the text.
It also said faith cannot be "imposed by force" and believers should not be "presumptuous".
Francis and Benedict, who both live within the walls of the Vatican City and wear the white papal vestments, met publicly on Friday at a ceremony in the Vatican for the unveiling of a new statue.
Benedict shocked the world in February when he became the first pontiff to resign of his own free will in 700 years of Church history.
Francis was elected by a conclave of cardinals to succeed him in March, becoming the first non-European pope in nearly 1,300 years.