Haider was abducted on May 9 while he was campaigning in his hometown of Multan in Punjab province for the elections. The kidnappers shot and killed his secretary and a bodyguard.
Police officials told the media that they arrested the suspect ring leader, identified as Wazir Gul, in Mardan district of the northwestern Khyber-Pakhtunkhwa province.
Gul is the brother of one of the six persons arrested in neighbouring Nowshera district yesterday.
During a raid in Akhora Khattak area of Nowshera district yesterday, police arrested four men and two women and freed another kidnapped man named Abdul Wahab.
Wahab, an activist of the PML-N party, said Haider and five other kidnapped persons had been held at the same place but the former premier's son was moved shortly before police raided the hideout.
He said Haider had been brought to the place in an injured condition.
Police officials claimed Wazir Gul was the head of an inter-provincial gang of kidnappers and was being questioned on the whereabouts of the former premier's son.
No group has claimed the kidnapping and the Gilani family has not been contacted by the abductors.
Punjab Police officials have said they believe a faction of the Punjabi Taliban kidnapped Ali Haider.
