Pecorelli, who was preparing to publish compromising information about Andreotti, was gunned down on March 20, 1979, while sitting in his car in central Rome. A gunman using a pistol fitted with a silencer shot him once in the head and three times in the back.
The murder remained unsolved until Andreotti was charged with the crime in 1999. Former mafia boss Tommaso Buscetta testified in the trial that Andreotti had asked the mob to have Pecorelli killed to prevent the journalist from publishing incriminating documents about the politician.
Andreotti, a towering figure in postWorld War II Italian politics who served as prime minister seven times, was initially acquitted of the crime but the appeals court in Perugia overturned that ruling.
The content of Pecorelli's allegations against the politician have never been clarified, The Associated Press reported.
Prime Minister Silvio Berlusconi criticized the ruling, saying it proves that Italian judges are biased against conservative politicians, and expressed hope that a higher court would overturn the conviction.