The attack in the northwestern province of Khyber Pakhtunkhwa follows a series of bombings at political rallies before the election, the most devastating of which was a suicide attack this month that killed 149 people in the southwestern province of Balochistan.
An election candidate and his driver were killed by a suicide bomber in northwest Pakistan on Sunday, police said, three days before the country's general election.
The district police chief Manzoor Afridi told Dawn News that at least eight to 10 kgs of explosive material was used in the attack.
He was campaigning for the northwestern Khyber-Pakhtunkhwa provincial assembly in the city of Dera Ismail Khan when the bomber detonated near his Land Cruiser.
The nation has been on edge over Wednesday's elections that will decide Pakistan's new prime minister after a string of similar suicide bombings this month against political candidates.
Four others, including Gandapur's guard, were injured.
Pakistan Muslim League-Nawaz (PML-N) president Shehbaz Sharif has said that people can change his name if he does not take Pakistan ahead of its arch-rival India after coming into power.
Violence in Pakistan has dropped significantly since the country's deadliest-ever militant attack, an assault on a school in the northwestern city of Peshawar in 2014 that killed more than 150 people, a lot of them children.
"Normally I don't say anything about Reham, but I will say this: I've made some mistakes in my life, but my second marriage has to be the biggest", the Pakistan Tehreek-e-Insaf chairman told the Mail Online in an interview.
Imran Khan is running to be next prime minister of Pakistan in July 25 elections.
According to police, unknown gunman opened fire at Durrani's vehicle in Mandio area of Bannu, when he was on his way to attend a public gathering.
The protestors raised several slogans against the ISI and claimed that the upcoming Pakistan elections 2018 are rigged and the result is already fixed.
Former minister Sardar Ikramullah Khan Gandapur was killed in a bomb blast near his auto in DI Khan on Sunday.