More than 40 people were injured. Most of the victims appeared to members of the opposition Pakistan People's Party, formerly headed by the slain Benazir Bhutto, said Mushtaq Hussain, an administrative official in the area.
He said a suicide bomber apparently "rammed his explosive-laden car into the election office," killing at least 14 and injuring more than 40.
"Several of our party members are lying in a pool of blood," said Zafar Ali, a party supporter at the scene. "We are taking the injured and dumping them into pickup vans to bring them to the hospital."
The attack in Parachinar, an area bordering Afghanistan, came two days before parliamentary elections considered crucial to restoring democracy in Pakistan after eight years of military rule under President Pervez Musharraf.
Monday's elections will take place against a backdrop of rising Islamic militancy throughout Pakistan, and many candidates have been discouraged from holding large rallies. Security fears are highest in lawless tribal areas along the Afghan border.