Sabrina de Sousa says she lost an appeal against extradition last week.
She is one of 26 Americans convicted in their absence for the abduction of Egyptian cleric Abu Omar.
He was allegedly flown to Egypt from Italy and tortured as part of the US extraordinary renditions programme.
Ms de Sousa said she was waiting to be informed when she will be transferred to Italy, where she has been sentenced to four-and-a-half years in jail.
Ms de Sousa was arrested in October on a European arrest warrant in Lisbon. She had appealed against extradition at the Supreme Court.
Many of the US citizens convicted with her in Italy have since been pardoned, and she would be the first CIA officer to be handed over to Italy.
Correspondents say it is not clear whether she will immediately be jailed or whether she might be granted a new trial.
Support for her cause is reported to come from an unusual source. In a recent interview with The Guardian, Abu Omar said that he believed that Ms de Souza and the other 25 Americans convicted in Italy have been made scapegoats and should be pardoned.
The cleric was taken to a US military base in Germany after his abduction and was later flown to Egypt where he says he was tortured.
He was eventually released in his home country, although an Italian court in 2013 is reported to have convicted him in absentia of terrorist activities.
A former CIA agent has said that she expects to be extradited imminently from Portugal to jail in Italy for her alleged role in the 2003 abduction of a terror suspect in Milan.