Accompanied by his son Ali Musa, Interior Minister Rehman Malik and other members of the cabinet, Gilani walked to the apex court as supporters threw rose petals on him.
Heavy security has been put into place with large deployment of commandos and anti-riot police.
The premier was charged with contempt by the apex court in February for refusing to write to the Swiss authorities to ask them to reopen corruption cases against President Asif Ali Zardari.
Gilani, 56, could face a six-month prison term and disqualification if he is convicted.
Gilani has appeared twice before in court and has maintained his innocence throughout, saying he had done nothing against the rules of business.
A seven-judge bench of the court, headed by Justice Nasirul Mulk, was to announce the verdict in the case.
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"The court has summoned me for the third time and I have decided to appear in the court tomorrow. I am doing this because I respect the judiciary and courts," Gilani had said yesterday.
The government has always respected the judiciary and acted on its orders and will continue to do so, he had said. PTI SAP AKJ