Mehmet Ali Agca, 46, was extradited to Turkey in 2000 after serving almost 20 years in prison in Italy for shooting and wounding the Pope in St Peter's Square in Rome. His motives for the attack remain unclear.
Agca was expected to be released as early as Moday, the semiofficial Anatolia news agency reported.
A Turkish court last week decided to free Mehmet Ali Agca "on parole on January 12," his lawyer, Mustafa Demirbag said today.
"We were hiding the decision but it is not a secret anymore," Mr Demirbag said.
"He was eligible to be released on parole because he had no disciplinary problems."
However Agca's sister, Fatma Agca, was surprised. "We did not hear it," said Fatma Agca from the family home in the southeastern city of Malatya.
Agca, a draft-dodger, was expected to be immediately enlisted by the military for obligatory military service, Anatolia said.
Upon his return to Turkey, Agca was sent to prison to serve a 10-year sentence for murdering Turkish journalist Abdi Ipekci in 1979. He was separately sentenced to seven years and four months for two robberies in Turkey the same year.
An Istanbul court ruled in 2004 that Agca should only serve the longest sentence, his conviction for killing Ipekci. That 10-year sentence was changed twice because of new Turkish laws.
Agca served less than six months in Turkish prison in 1979 for killing Ipekci before he escaped, resurfacing in 1981 in Rome.
Because of the time he served in the past, the Turkish prison asked for permission from a court to release Agca. The court ruled that Agca could now be freed within the next week, Anatolia said.
Vatican accepts decision
The Vatican said that it accepted the decision by the Turkish court to release Agca.
"With legal issues, the Holy See leaves it up to the courts with competence in these areas," Vatican spokesman Joaquin Navarro-Valls said.
He said the Vatican had only learned of the court's decision from press agencies and had not been given prior notice.
Agc was a 23-year-old far-right militant on the run from the Turkish police when he opened fire in Rome.
The pope suffered a serious wound to the abdomen. John Paul II forgave his attacker and even met him in prison.
Agca reportedly sympathised with the Gray Wolves, a far right-wing militant group that fought street battles against leftists in the 1970s.