Sabrina de Sousa, 60, was set to be extradited to Italy in the coming days to face justice over the abduction of radical preacher Abu Omar in Milan, after she was arrested in Portugal last week.
She had gone on trial in absentia along with 22 others in what were the first legal convictions in the world against people involved in the CIA's extraordinary renditions programme that followed the September 11, 2001 attacks.
But Italian President Sergio Mattarella has granted her "a partial pardon of one year's imprisonment", reducing her jail time to three years of a lenient form of sentence that does not necessarily need to be served behind bars and allows the convict to work.
Mattarella's statement notably did not mention plans to extradite de Sousa, and he said her sentence -- which would no longer involve physical detention -- could potentially be further relaxed.
The presidency said it had "taken into account the attitude of the convicted, the fact that the United States has stopped the practice of extraordinary rendition, and the need to rebalance the sentence with those of other people convicted for the same offence."
Omar was kidnapped from a Milan street on February 17, 2003 in an operation allegedly led jointly by the CIA and the Italian intelligence services.
He was then transfered to Egypt where his lawyers say he was tortured, in a case that highlighted the controversial secret renditions of suspected radicals by the United States and its allies.
De Sousa has said she served as an interpreter for the CIA team that organised Omar's abduction but denies any direct role in the operation.