Pakistan's Supreme Court found Gilani guilty Thursday of contempt of court for refusing to bring back old corruption charges against President Asif Ali Zardari, CNN reported.
The contempt charge stems from Gilani failing to ask Swiss authorities to reopen charges against Zardari, who allegedly laundered tens of millions of dollars while his wife, Benazir Bhutto, served as prime minister.
The prime minister was not sentenced by the Supreme Court and can only be forced to step down by Parliament, leaving the country in limbo, experts say.
"It plunges the country into political and legal crisis," said Najam Sethi, editor of the English-language political weekly The Friday Times.
Gilani's main political opponent, Nawaz Sharif, a former premier looking to retake the position in the country's elections next year, called for the prime minister to step down.
"I think that after the conviction the PM should immediately step down from his post," Sharif said following Thursday's verdict. "This is a convicted prime minister. He has been found guilty, he has been sentenced by the Supreme Court."
Ahmed Bilal Mehboob, the head of an Islamabad political think tank, said Gilani's conviction failed to answer questions about Zardari's case.
"It has diverted attention from the real issue," he said. "The real issue is if our president is guilty of amassing illegitimate wealth and money laundering. We have failed to arrive at any conclusion and we're still perceived as a nation that doesn't abide by the rule of law."