The court's latest decision came after prosecutors filed a case review, presenting what they said was fresh evidence that Priyanto served Munir with a poison-laced drink while in transit in Singapore's Changi Airport.
Nurhadi, a court spokesman, said: "Pollycarpus has been proven legally and without a doubt to have committed premeditated murder and letter forgery."
Suciwati, Munir's widow, said the verdict did not go far enough.
She said: "This is what he deserves, but I wish he got a longer punishment. What is more important is to follow up on the intelligence people behind him. [Pollycarpus] did not act on his own."
Pollycarpus, who has always denied any wrong doing, told local radio that he was shocked by the ruling, describing the process as "a soap opera".
He said: "I have been made a scapegoat. It is very clear."
Mohammad Assegaf, Pollycarpus' lawyer, contested the legality of the decision because "only a defendant can file a case review, not prosecutors".
Separately, prosecutors demanded an 18-month prison sentence for Indra Setiawan, the former head of Garuda, Indonesia's national carrierfor aiding Pollycarpus in the murder of Munir.
Indra had previously told the central Jakarta district court that before Munir's death he had received a letter from Indonesia's spy agency asking him to allow Pollycarpus to be an aviation security officer.
But Setiawan has said he lost the letter, which was signed by a deputy chief of the agency, and Antawirya Dipodiputro, his lawyer, said that his client had no knowledge about Pollycarpus' plans.
The murder of Munir has drawn widespread international attention and is seen as a test of the government's determination to uphold the rule of law, as well as the accountability of several state agencies, including the spy agency.