The blast - which was claimed by the Islamic State group - ripped through the crowd in the town of Mastung near the Balochistan provincial capital Quetta.
He has served as the federal minister for housing and works in the last federal government and is also a former chief minister of Khyber Pakhtunkhwa.
Baluchistan Home Minister Agha Omer Bangulzai told Reuters that the death toll in the attack had risen to 128 people, with over 150 wounded.
Sharif is expected to appeal against his conviction and seek bail.
Sharif and Maryam were earlier this month sentenced to 10 years and seven years in prison, respectively, over the purchase of upscale London flats.
"The Pakistani authorities have a duty to protect the rights of all Pakistanis during this election period their physical security and their ability to express their political views freely, regardless of which party they belong to", said Omar Waraich, deputy South Asia director at Amnesty International.
Men mourn the death of relatives and party workers, who were killed after a suicide attack during an election campaign meeting, at hospital morgue in Quetta, Pakistan July 13, 2018.
During his term in office, Sharif criticised the military's involvement in civilian affairs and its efforts in fighting extremists.
Durrani is standing against cricketer-turned-politician Imran Khan, whose Pakistan Tehreek-e-Insaf party (PTI) is one of the frontrunners in the July 25 vote. The military denied the accusations saying their assistance in carrying out the elections was requested by Pakistan's Election Commission. The army will deploy 350,000 security personnel to polling stations throughout the country on election day. This was the first major incident of violence ahead of the elections in Pakistan.
District Police Officer Bannu Khurram Rashid has said the incident took place as Durrani was returning from an election rally and explosives were detonated close to his vehicle with the help of remote control.
Durrani is running in the July 25 vote against popular former lawmaker Imran Khan.
The JUI-F central general secretary, who is contesting for the upcoming polls under Muttahida Majlise-e-Amal (MMA), is reported to have remained unhurt in the attack.
Raisani is the second electoral candidate to be killed in pre-election violence this week.
Another 45 people were hurt in the attack in Mastung, a town in southwest Baluchistan province.
Earlier he had also confirmed that the blast was carried out by a suicide bomber and that the explosion had killed Siraj Raisani, who was running for a provincial seat with the newly formed Balochistan Awami Party (BAP).