Awami National Party (ANP) candidate Barrister Haroon Bilour was among the deceased. The blast also wounded many people, Geo News reported, citing police.
The explosion occurred moments after Bilour arrived at the venue, near the stage, to address supporters at the meeting as welcoming party members and admirers engaged in a display of fireworks, which the bomber made use of as his cover.
The late ANP candidate was set to contest the July 25 elections from Peshawar's PK-78 constituency.
Nearly eight kilos of TNT explosives were used in the blast, Qazi Jamil, the capital city police officer (CCPO) of Peshawar said.
The Bomb Disposal Squad (BDS) confirmed that the blast was a suicide attack.
Speaking about the incident, Chief Election Commissioner (CEC) Justice (retired) Sardar Mohammad Raza Khan condemned the terrorist attack and termed it a "weakness of security institutions".
The attack was a conspiracy against the transparent elections, the CEC said, noting that the provincial governments were ordered to provide fool-proof security to all candidates.
On the other hand, ANP leader Mian Iftikhar Hussain said the government had failed to provide security to the party.
"Perhaps someone wishes to sabotage the elections... wants to push ANP out of the electoral race," he said.
However, the "ANP will fully participate in the elections", he added.