The process of beatification, or declaring the late pontiff to be "blessed", is a crucial step towards making him a saint.
John Paul II died in 2005 after a papacy of nearly 27 years.
The Vatican credits him with the miraculous cure of a nun said to have had Parkinson's Disease.
Church officials believe that the Polish pope, who himself suffered from the condition, interceded for the miraculous cure of Sister Marie Simon-Pierre, a Frenchwoman in her late forties.
She has said her illness inexplicably disappeared two months after John Paul II's death, after she and her fellow nuns had prayed to him.
Church-appointed doctors agreed that there was no medical explanation for the curing of the nun, although last year there were some doubts about the validity of the miracle.
The 'miracle' that clinched the  beatification
A Polish newspaper said that a doctor who scrutinised the nun's case had concluded that she might have been suffering not from Parkinson's, but from a nervous disorder from which temporary recovery is medically possible.
Up to a million people are expected to gather in Rome for the beatification.
Mourners at John Paul II's funeral on 8 April 2005 chanted: "Santo subito!" - or "Make him a saint right now!"
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The following month, Pope Benedict put him on a fast track to sainthood by dispensing with Church rules that normally impose a five-year waiting period after a candidate's death before the beatification procedure can start.
Work is under way in St Peter's Basilica to make space for John Paul II's tomb since, in accordance with tradition, the remains of popes who are beatified are moved up from the crypt to the nave.
"John Paul II's coffin will be moved in St Peter's Basilica from the Vatican crypt without being opened," said Vatican spokesman Federico Lombardi.
His body will not be displayed but placed in a tomb under a simple marble stone reading "Beatus Ioannes Paulus II" (Blessed John Paul II).
In order for John Paul II to be canonised as a saint, a second miracle would have to be verified following the beatification.
Pope Benedict XVI has formally approved a miracle attributed to his late predecessor, paving the way to John Paul II's beatification on 1 May.