Political parties and the government in Pakistan have condemned the attack, with caretaker prime minister Nasirul Mulk ordering authorities to step up security ahead of the general election on 25 July.
Bashir Bilour, the father of Haroon, was also martyred in a suicide bombing targeting his rally in the fabled Qissa Khawani bazaar of Peshawar in December 2012.
Officials said at least 54 people were wounded.
People carry the coffins of the victims of a suicide bombing at an election rally for burial in Peshawar, Pakistan, on Wednesday.
The police officer did not confirm the nature of the blast, however, a local ANP leader while talking to DawnNewsTV said that a suicide bomber blew himself when Bilour entered the compound where the meeting was being held.
The explosion took place moments after Bilour arrived at the spot to address supporters.
Hospital's spokesperson Zulfiqar Ali Baba Khel reportedly said that 13 people died and more than 47 are wounded in the blast. Some people were seen crying.
Militants have targeted politicians, religious gatherings, security forces and even schools in Peshawar. The deceased ANP candidate, who was set to contest the July 25 elections from Peshawar's PK-78 constituency, will be buried in Wazir Bagh at 5 pm today (Wednesday).
"I lost consciousness after the blast".
Party workers cried and hugged, while others looked on in shock as funeral prayers were said.
But ANP leaders have vowed to continue their campaign this year despite the bombing in Peshawar.
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.
"Political differences apart, all political parties and their candidates must be provided proper security during their election campaigns by the state", he said in a tweet. Officials have said that while the threat remains, terrorists have been significantly weakened because of military operations in recent years. No group has claimed responsibility of the attack.