At least 30 people were wounded in the blast, which occurred just after the rally hosted by the JUI-F religious political party ended on Friday morning, said a police official, speaking on condition of anonymity.
Sharif's arrival in the eastern city of Lahore was delayed until 8pm.
The bomb targeted the convoy of the Muttahida Majlis-e-Amal (MMA) candidate Akram Khan Durrani, who survived the attack, police said. He will be accompanied by his daughter Mariam, who has been sentenced to seven years in prison.
All roads leading to the airport and entry points into Lahore from adjoining areas were barricaded to prevent a large turnout of PML (N) supporters at the airport.
Sharif has been banned from participating in politics, and his brother Shahbaz Sharif now heads the Pakistan Muslim League and is campaigning for re-election on 25 July.
In February 2017, Islamic State claimed responsibility for a suicide bombing at a shrine in southern Pakistan, killing 83 people and wounding over 150.
It came hours after another bomb killed at least four people at a campaign rally in Bannu in the country's northwest. The army will deploy 350,000 security personnel to polling stations on election day.
It was the latest in a string of attacks that have spurred fears of violence ahead of nationwide polls on July 25, and underscored the fragility of Pakistan's dramatic gains in security.
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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.
Mr Durrani is running against popular former MP Imran Khan.
The second explosion was in southwestern Baluchistan province, that killed 65 people and critically wounded the candidate.
Akram Khan Durrani, a former CM of Khyber-Pakhtunkhwa, remained unhurt in the attack.
"There seems to be a conspiracy to sabotage the 25 July elections but the people of Pakistan will not allow any design meant to target these historic elections to succeed", he tweeted.
The blast comes days after a bomb claimed by the Tehreek-e-Taliban targeted a rally by the Awami National Party (ANP) in the city of Peshawar on Tuesday.
"What credibility will these elections have when the government is taking such a drastic action against our people and this crackdown is taking place all over the country?" he told Reuters at the airport in Abu Dhabi as he waited for a connecting flight to Lahore.