The roadshow via the iconic Grand Trunk Road, which links a large part of South Asia from Bangladesh to Afghanistan, comes despite security threats, drawing thousands of supporters on its way to the provincial capital of Punjab.
On Monday, a bomb blast ripped through the route Sharif was earlier planned to take in Lahore, killing two people.
The ruling Pakistan Muslim League-Nawaz party sources said some leaders were concerned about Sharif's security and saw the blast as a "message" to Sharif to tone down his rally.
The 370-km journey began around noon from Punjab House in Islamabad, after being delayed by up to three hours.
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Sharif was seen off by his successor Prime Minister Shahid Khaqan Abbasi, Cabinet ministers, other party leaders and hundreds of his supporters. Soon after, Sharif's convoy swelled to hundreds of vehicles and several thousands of supporters, making it impossible for them to move quickly.
A plan to address supporters in Islamabad was cancelled due to security reasons and paucity of time, party leaders said.
The procession moved at an unusually slow pace, reaching the garrison city of Rawalpindi, a 20-minute drive, in four hours, where thousands of supporters waited for Sharif.
Asif Kirmani, Sharif's spokesman, said "a sea of people" welcomed Sharif. Punjab Law Minister Rana Sanaullah asserted Sharif's would be the biggest rally in Pakistan's history.
Qamar Zaman Kaira of Pakistan Peoples Party (PPP) said that there could be around 10,000 people with Sharif. And Imran Khan's Pakistan Tehreek-e-Insaf said that Sharif failed to bring out people and the rally was already a "flop show."
Authorities estimated that up to 8,500 people and 950 vehicles were part of Sharif's procession, reports said.
Sharif was expected to stay put at Rawalpindi tonight and resume his journey tomorrow morning from the garrison city.
Several other smaller rallies joined Sharif's on the way.
The procession was earlier expected to reach Lahore in two days but given today's progress it was unlikely to happen.
Massive security arrangements have been put in place on the route. A special bomb-proof vehicle has been arranged for Sharif, who briefly travelled in the vehicle, spending most of the time in his car.
"Security is an issue, though elaborate measures have been taken to make the journey free of any risk," a PML-N leader said.
But Sharif has brushed aside such concerns and told party leaders that it was vital to speak to supporters about the circumstances under which he was ousted, party sources said.
Earlier today, Sharif held a meeting with his successor, Prime Minister Shahid Khaqan Abbasi, Cabinet ministers and party leaders before embarking on the long journey.
He has not visited Lahore, his hometown, since his ouster from the government. The former prime minister also planned to deliver speeches at key places during the journey.
Last month, a five-member apex bench had found Sharif "unfit to hold office", ruling that he had been "dishonest to the parliament and the courts in not disclosing his employment in the Dubai-based Capital FZE company in his 2013 nomination papers."
Sharif's travel plan has upset his rival Imran Khan, who in a press conference, has alleged that Sharif was disgracing the court by challenging its decision through the roadshow.
"It is strange that a man who has been disqualified is planning to...Tell people he is innocent," said the cricketer- turned-politician.
Canada-based cleric of Pakistani-origin Tahir-ul-Qadri returned to Lahore ahead of the rally. He has criticised Sharif's roadshow.