Saddiq Zaman Khattak was a businessman and a candidate for the Awami National Party (ANP), the leading secular party in Pakistan's ethnic Pastun northwest.
A party leader said he had previously received threats.
Pakistani Taliban claimed responsibility for the attack and threatened further attacks on the ANP and its outgoing coalition partners, the Pakistan People's Party and MQM, the main party in Karachi.
"We have attacked him and we will continue such attacks in the future. ANP, People's Party and MQM are our targets," Taliban spokesman Ehsanullah Ehsan told AFP.
Musharraf party to boycott electionThe party of former Pakistani military ruler Pervez Musharraf, who is facing a barrage of legal cases over his time in power, on Friday announced it will boycott next week's historic election.
Ex-president has been humiliated since returning in March from self-imposed exile and is currently under house arrest.