Pope Benedict’s former butler is to be moved from house arrest to serve his remaining sentence in a Vatican jail cell.
Paolo Gabriele was convicted of stealing papal documents and leaking them to the media earlier this month.
A Vatican statement said Gabriele would move to a police station to complete his sentence.
It said Gabriele would still be able to appeal to the Pope for a pardon, which would free him from jail.
However, it said Gabriele must first recognise the gravity of his crime and "make a sincere request for forgiveness from the Supreme Pontiff and those who were unjustly offended".
The Vatican said the decision to end house arrest for Gabriele, who has been living with his family in their apartment in the Vatican, was taken after both the defence and the prosecution decided not to appeal the sentence.
Gabriele, who was responsible for the most serious security breach in recent Vatican history, was sentenced to 18 months on 6 October.
The prosecution had asked for a three-year term but the court gave him a lighter sentence because he had no previous criminal record.
Gabriele, 46, who served the pope his meals and helped him dress, leaked private documents to the media.
Some of them alleged corruption in the Vatican's business dealings with Italian companies and internal conflict over the running of the Vatican bank.
The Vatican has no jail as such but has cells in the police station inside the tiny city-state.