Mr Bilour's father, Bashir Ahmed Bilour, also a senior figure within the leftist secular party, was killed in a Taliban suicide blast at a party meeting in 2012.
Confirming Haroon Bilour's martyrdom, the spokesman said that Haroon's son, Danial Bilour, was safe.
The blast occurred near the vehicle of Bilour in Yakatoot area of Peshwar. Bilour suffered serious injuries and was shifted to the hospital where he succumbed to his wounds.
A suicide bomber blew himself up at a corner meeting late last night moments after Haroon Bilour entered to a joyous welcome marked by fireworks, which the assailant used as their cover, killing at least 14 and wounding 65 others, 15 of whom were in critical condition.
Following the blast, security forces reached the spot and cordoned off the area.
11 others were martyred and 35 injured in the suicide bomb attack targeting his rally in a congested neighbourhood of the Khyber-Pakhtunkhwa capital shortly before the midnight.
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Terming it the "peak of terrorism", ANP leader Mian Iftikhar Hussain said the attack is aimed at derailing democratic system in the country and a conspiracy to delay upcoming general elections. The TTP spokesperson at the time, Ehsanullah Ehsan, had told journalists that Haroon was the target, but "unfortunately Ghulam Ahmed Bilour got injured".
The ANP was the main target of Taliban attacks in the 2013 election. The militants killed hundreds of ANP leaders and supporters in attacks around the 2013 election.
Bashir was targeted in the Qisa Khwani Bazaar during an electioneering rally.
There was no immediate claim of responsibility for Tuesday's attack.
Pakistan Tehreek-e-Insaf (PTI) chief Imran Khan strongly condemned the attack at the ANP corner meeting.
He said Nacta had forwarded 12 threat alerts to the federal interior and provincial home ministries as well as law enforcement agencies.