Pope to deliver Thought For Day.
Former station controller Mark Damazer said earlier this year that persuading Pope Benedict XVI to make an appearance was on his wish list.
However the Papal visit to the UK three months ago passed without him recording a message for the slot.
The Pope's message will be broadcast at 7.45am during the Today programme.
It is the first time the Pope has presented material which has been specifically written for a broadcast audience. He recorded his Thought For The Day in Rome earlier yesterday.
Gwyneth Williams, the new controller of Radio 4, said: "I'm delighted Pope Benedict is sharing his Christmas message with the Radio 4 audience.
Thought For The Day allows speakers from a range of faiths to give a personal reflection and has been broadcast since 1970.
But Terry Sanderson, president of the National Secular Society, attacked the BBC. He said: "The BBC is giving the Pope an unquestioned slot to continue whitewashing his Church's disgraceful record on covering up child abuse by its priests."
The Pope will deliver a message on Radio 4