Judge Giuseppe Dalla Torre read the verdict aloud two hours after the three-judge panel began deliberating Paolo Gabriele's fate.
The sentence was reduced to 18 months from three years because of a series of mitigating circumstances, including that Gabriele had no previous record, had worked for years for the Holy See, acknowledged that he had betrayed the pope and was convinced, "albeit erroneously" that he was doing the right thing, Dalla Torre said.
Gabriele was accused of stealing the pope's private correspondence and passing it on to journalist Gianluigi Nuzzi, whose book revealed the intrigue, petty infighting and allegations of corruption and homosexual liaisons that plague the leadership of the Roman Catholic Church.
In his final appeal to the court Saturday morning, Gabriele insisted "I don't feel like a thief" and said he leaked the pope's private correspondence out of a "visceral love" for the church and the pope. He has said he felt the pope wasn't being informed of the "evil and corruption" in the Vatican, and that exposing the problems would put the church back on the right track.
Gabriele's attorney, Cristiana Arru, said the sentence was "good, balanced" and said she was awaiting the judges' written reasoning before deciding whether to appeal.
Nuzzi's book, "His Holiness: Pope Benedict XVI's Secret Papers" convulsed the Vatican for months and prompted an unprecedented response, with the pope naming a commission of cardinals to investigate the origin of the leaks alongside Vatican magistrates.
Arru said Gabriele would return to his Vatican City apartment to begin serving his sentence. He has been held on house arrest there since July after spending his first two months in a Vatican detention room.
Gabriele was also ordered to pay court costs.
A papal pardon is widely expected, though it's not known when it might be granted.
In her closing arguments, Arru insisted that only photocopies, not original documents, were taken from the Apostolic Palace, disputing testimony from the pope's secretary who said he saw original letters in the evidence seized from Gabriele's home.
She admitted Gabriele's gesture was "condemnable" but said it was a misappropriation of documents, not theft, and that as a result Gabriele should serve no time for the lesser crime.