Agca, 48, was taken straight from jail to a military recruitment office, his lawyer said, because the Turkish army wants to claim him for missed service, a legal obligation for Turkish men.
Mustafa Demirbag said: "We are now at the military recruitment office. The procedure for his military service has started. We are waiting for the results."
Agca served 19 years in an Italian prison for the assassination attempt before being pardoned at the Pope's behest in 2000. He was then extradited to Turkey to serve a separate sentence in an Istanbul jail for robbery and murder.
Under new Turkish laws, his time served in Italy was deducted from the 25 years left on his sentence in Turkey for the murder of Abdi Ipekci, a liberal newspaper editor, in 1979.
Agca has given conflicting reasons why he shot the Pope St Peter's Square in Rome. At his trial in 1986, prosecutors tried but failed to prove that Agca had been hired by Bulgaria's secret service to kill the Pope on behalf of the Soviet Union.