Nawabzada Siraj Raisani, who was campaigning for an assembly seat in the southern province of Balochistan, was killed in the bomb blast along with dozens of others, Balochistan Home Secretary Haider Ali Shikoh told CNN. Another senior official, Qaim Lashari, also confirmed it was a suicide blast.
The Islamic State's Amaq News Agency claimed that the group was responsible for carrying out the bombing. The bombing was the biggest attack in Pakistan in over a year and is the third incident of election-related violence this week.
In a televised appeal to supporters from London earlier this week, Sharif said he was not afraid of prison and asked people to vote for his party.
Among the dead was Siraj Raisani, who was running for a provincial seat with the newly-formed local Balochistan Awami Party (BAP), Bungalzai said.
Raisani was the younger brother of former provincial chief minister Mir Aslam Raisani.
The Mastung bombing was the latest, and deadliest, of a string of attacks targeting politically exposed persons ahead of the 25 July election.
Police and witnesses said Durrani was traveling in a convoy when a remote-controlled bomb planted in a parked motorcycle exploded near his vehicle.That attack killed four people and injured almost 40 others but Durrani escaped unhurt.The politician is a central leader of a main religious party, Jamiat Ulema-e-Islam-F (JUI-F).
On Monday, a suicide bomber killed Awami National Party (ANP) leader and candidate in the general elections, Haroon Bilour and 19 others after striking at a corner election meeting in Peshawar city. Hospital officials said on Friday that the toll in that attack had risen to 22. Other local authorities confirmed the attack.
Durrani belongs to an alliance of religious groups called Muttahida Majlis-e-Amal, which ruled the province between 2002 and 2008 under him. But he said the people of Pakistan will not allow anything to prevent "historic" elections from taking place.
Pakistan's caretaker government has launched a crackdown on political gatherings.
Strongly condemning the terrorist attack on Durrani, Pakistan Tehreek-e-Insaf (PTI) chief Imran Khan expressed sorrow over the loss of precious lives.
Analysts warn however that Pakistan has yet to tackle the root causes of militancy.
The twin attacks came as former prime minister Nawaz Sharif along with his daughter Maryam returned to the country to face arrest in a corruption case.
Pakistan People's Party (PPP) Chairman Bilawal Bhutto-Zardari demanded that the security of contesting candidates be ensured.