Sharif and his daughter Maryam both face arrest when they arrive back in Lahore from London on Friday.
The three-term PM was ousted from office last year after a corruption investigation. He was sentenced in absentia to 10 years last week.
He has accused Pakistan's security establishment of conspiring against him ahead of July 25 elections.
"There was a time when we used to say a state within a state, now it's a state above the state," he told supporters of his Pakistan Muslim League-Nawaz (PML-N) party in London on Wednesday.
"Despite seeing the bars of prison in front of my eyes, I am going to Pakistan."
Thousands of supporters are expected to flock to the airport to greet Mr Sharif, who was convicted by an anti-corruption court last week over his family's ownership of four luxury flats in London.
Hundreds of party activists in Lahore are reported to have been detained ahead of his return.
He has called for a "mass gathering of the people".
Sharif, 67, has been one of the country's leading politicians for most of the past 30 years. His party has blamed the military for being behind his conviction, saying it is going after the PML-N for its criticism of the security establishment and the party's policy to improve ties with India.
In May, the Dawn newspaper published an interview with Sharif in which he questioned the wisdom of "allowing" Pakistani militants to cross the border and kill 150 people in Mumbai, referring to attacks in the Indian business capital in 2008.
The military, which has ruled Pakistan for about half of its 70-year post-independence history, has denied it has any "direct role" in the elections or the political process.
Although he was disqualified from standing in the upcoming election by the Supreme Court, Sharif remains one of the most popular politicians in Pakistan, especially in Punjab, the most populous and electorally significant province.
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