Authorities in Venezuela had asked Interpol to locate and arrest Ramirez in 2018 and subsequently demanded his extradition from Italy in 2020 in connection with embezzlement charges.
Ramirez, who denies the corruption allegations, says President Nicolas Maduro's administration is seeking to smear him over his anti-government comments.
"The Italian Supreme Court has declared definitively inadmissible the extradition request," Ramirez's Italian lawyer Roberto De Vita told Reuters.
He said the court had backed a previous ruling that Ramirez could not be sent back to Venezuela because of human rights violations in the South American state.
Court rulings in Italy are initially delivered to those involved in the case and the verdict has not yet been published on the Supreme Court website.
Ramirez served for a decade as oil minister and president of state oil company PDVSA, which controls some of the largest crude reserves in the world.
Venezuela's Supreme Court said on Facebook in 2020 that Ramirez faced criminal charges including embezzlement and bid-rigging for oil contracts.
He was ousted from his post as Venezuela's U.N. envoy in 2017 after publicly criticizing Maduro and the status of the OPEC nation's oil industry.
Ramirez had been a close confidant and remains an admirer of the late former president Hugo Chavez, Maduro's predecessor and mentor.
(Reporting by Marco Carta; Writing by Crispian Balmer; Editing by Mike Harrison)