Akhtar Shah, a member of the Pakistan Social Justice Party, argued that Pervez Musharraf, as a former president, could not be held responsible in the case and had immunity, Dawn News reported.
A Federal Investigative Agency prosecutor opposed the application, saying Akhtar Shah could not become a party in the case.
The court reserved judgment on the application seeking to prevent Musharraf from becoming a party in the case and eventually dismissed the request, Dawn News said.
The judges did accept a request for a new trial of the case and ordered the FIA to present a list of witnesses at the next hearing, scheduled for Oct. 22.
Bhutto was assassinated in a gun-and-bomb attack in Rawalpindi on Dec. 27, 2007. She was killed after addressing an election campaign rally.