The showdown between Pakistan's highest court and Prime Minister Yousuf Raza Gilani is over, with the court convicting Mr. Gilani of contempt.

The Supreme Court issued its verdict Thursday in Islamabad, ruling the prime minister openly defied the court's order to reopen an old corruption case against President Asif Ali Zardari. But the high court spared Mr. Gilani any time in prison, saying the sentence against him would only stand until the judges left the chamber.

The prime minister could have been sent to prison for up to six months. Mr. Gilani's conviction means there are now grounds to disqualify him from parliament. The parliamentary speaker and election commission must now decide whether he can be dismissed as a lawmaker, and thus as prime minister.

The prime minister's lawyer, Aitzaz Ahsan, later told reporters his client will appeal the Supreme Court ruling once he receives the detailed court order. He maintains that Mr. Gilani was convicted on a charge for which he was never indicted — scandalizing the judiciary.

Thursday's ruling sparked protests from Mr. Gilani's supporters and members of his Pakistan People's Party in Karachi and other cities.

Opposition leaders, including former Prime Minister Nawaz Sharif, called on Mr. Gilani to step down — saying they will no longer accept him as Pakistan's prime minister.

Pakistani attorney Babar Sattar refers to the high court verdict as a “rap on the knuckles.”

Sattar said, “From an ethical and a moral standpoint, he (Mr. Gilani) has lost the kind of moral authority to continue to rule.” But he also said the verdict struck a careful balance, showing that court verdicts must be upheld “while not creating consequences by punishing him in a way that would create a crisis of governance.”

Thursday's guilty verdict is the latest development in what has been an ongoing battle between the court and the prime minister over the status of corruption cases dating back to the 1990s.

Prosecutors accuse President Zardari, former prime minister Benazir Bhutto and others of laundering millions of dollars through Swiss bank accounts. Ms. Bhutto, President Zardari's wife, was assassinated in 2007.

Charges against Mr. Zardari and the others were dropped after a 2007 amnesty agreement, but the court struck down the deal in 2009 and has been battling to reopen the cases ever since.

Prime Minister Gilani had refused to cooperate, arguing instead that the president has legal immunity while in office.