In dismissing the motion Wednesday, U.S. District Judge George Daniels said the plaintiffs' allegations met the requirements for the court to assume jurisdiction under the Justice Against Sponsors of Terrorism Act.
Congress passed the act in 2016 over President Barack Obama's veto, allowing the claims to go forward after they were rejected once in court. The Saudis had argued that the kingdom was protected by sovereign immunity. In addition, the kingdom has long denied any involvement in the attacks.
The Center City-based Cozen O'Connor law firm has taken the lead in much of the litigation, filing one of the first lawsuits in 2003.
"It's a historic turn of events," said Sean Carter, Cozen's lead litigator in the lawsuit. "After a 15-year legal battle, for the first time the court has said the Saudis will have to participate in discovery."
Two commercial airliners piloted by terrorists crashed into the twin towers of the World Trade Center in New York City. A third jet hit the Pentagon, and a fourth plane crashed into a field in Somerset County, Pa. Fifteen of the 19 attackers were Saudis.
Hundreds of victims' relatives and injured survivors, along with insurance companies and businesses, sued the Saudi government, saying its employees knowingly assisted hijackers who carried out the attacks.
"The families are elated that they at last have the opportunity to proceed with a legal process that will ensure the truth comes out," Carter said.
Carter said Saudi Arabia has argued for years that the kingdom was exonerated by the 9/11 Commission.
"That's the other piece of the judge's ruling that's significant," Carter said. "That wasn't the case. But there's been a massive PR campaign. The Saudis were never exonerated. The court looked at that and said there's nothing in the commission report that supports their claim."