Police said the bomber struck when Bilour was about to address some 200 supporters.
Another 65 people were wounded.
"According to our initial investigation, it was a suicide attack and Haroon Bilour. was the target", police official Shafqat Malik told AFP.
The head of Peshawar city police also informed media representatives that some 8 kilograms of explosives were used in the attack.
The Associated Press further notes, "Islamic extremists grew to despise the ANP when it ruled the Khyber Pakhtunkhwa province, of which Peshawar is the capital, from 2008 to 2013".
During that time the military waged a major offensive against militants in the Swat Valley.
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Mohammad Khurasani, a spokesman for the PakistaniTaliban, said in a statement that they targeted ANP's rally, killing Bilour, a candidate for a seat in the provincial legislature in Peshawar.
No one immediately claimed responsibility for the attack, but there have been dozens of such bombings in recent years in Peshawar.
An army spokesperson said on Tuesday the military will deploy more than 371,000 security forces to polling stations to ensure free, fair and transparent national elections on July 25.
Fireworks were being burst as the ANP candidate from PK 78 constituency arrived on the stage when the suicide bomber blew himself up. He suffered serious injuries and was shifted to hospital where he succumbed to his wounds.
His body was later taken to Bilour House where party workers paid tributes to him.
Although there has been no immediate claim of responsibility for the attack, the city of Peshawar has for decades been a victim of militancy due to its status as a frontline for the ongoing war against terrorism as well as its proximity to the restless tribal areas and the Pak-Afghan border. The Pakistan Muslim League (N) leads most opinion polls, with the Pakistan Tehreek-e-Insaf (PTI) in second, followed by the Pakistan Peoples Party.
Bilour's family called on his supporters to remain calm.
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