Details were still coming to light, but the ruling Friday could invalidate the appointments of judges by Musharraf in the six weeks after he suspended the constitution on Nov. 3, 2007.
It also may strengthen the case for bringing treason charges against him.
Musharraf, a longtime U.S. ally, declared the emergency when it appeared the Supreme Court might have challenged his eligibility for office.
Eventually, Musharraf allowed elections that brought his foes to power. He stepped down in August 2008. Ever since, many opponents have demanded he be held accountable.