Senior police official Qaim Lashari had earlier said that more than 1000 people were in attendance at the rally in the town of Mastung in the violence-plagued province of Baluchistan.
No group has yet claimed responsibility for that attack.
The suicide bombing was the second election-related violence to take place on Friday.
Durrani, who was heading back from an election rally near North Waziristan, remained safe in the remote control blast, District Police Officer (DPO) Bannu Khurram Rasheed said.
Among the dead was Siraj Raisani, who was running for a provincial seat with the newly-formed local Balochistan Awami Party (BAP), Bungalzai said.
"Mir Siraj Raisani succumbed to wounds while he was being shifted to Quetta", he added.
The deadly suicide attack which ripped through a political rally of Balochistan Awami Party (BAP) is claimed to have been carried out by the Islamic State and has taken lives of over 128 people, including BAP leader and candidate Nawabzada Siraj Raisani from PB-35 (Mastung). Hospital officials said Friday that the toll in that attack had risen to 22.More news: Trump refuses to answer CNN reporter's question
In February 2017, Islamic State claimed responsibility for a suicide bombing at a shrine in southern Pakistan, killing 83 people and wounding over 150.
The bomb targeted the convoy of the Muttahida Majlis-e-Amal (MMA) candidate Akram Khan Durrani, who survived the attack, police said.
Haroon Bilour, a senior secular politician and candidate for a provincial assembly seat, was among those killed in Tuesday's bombing.
The election will pit the PML-N against its main rival, the Pakistan Tehreek-e-Insaf, a party led by cricket star-turned-politician Imran Khan.
Pakistan's caretaker government has launched a crackdown on political gatherings.
Pakistani Taliban have been targeting the members and the leaders of Durrani's party in the past for the religious group's support and participation in the democratic process, which the militants say is a system brought in by Western infidels.
But security across the country has dramatically improved since government and military operations cleared large swathes of territory near the Afghan border in recent years.