"The appeal is dismissed," Chief Justice Iftikhar Chaudhry said in court, reading the decision of the eight-member bench.
The legal tussle stems from thousands of old corruption cases thrown out in 2007 by a controversial amnesty law passed under former military president Pervez Musharraf.
The contempt accusation arises from Gilani and his advisers ignoring court orders to ask Swiss authorities to re-open cases against President Asif Ali Zardari, the most prominent beneficiary of the law.
If convicted, Gilani could face jail, but the case, which has raised tension between Pakistan's civilian leaders and the Supreme Court, could drag on and paralyse decision-making.
