Regarding the much-debated rigging allegations, Imran expressed that those having reservations should move to the election commission of Pakistan or the Supreme Court.
Mr Khan received 176 votes in the 342-seat National Assembly, said the speaker of the parliament, Asad Qaiser.
Khan saw his party sweep to victory in a July 25 general election promising to fight corruption and lift millions of people out of poverty.
Khan's election was only the second democratic transfer of power since Pakistan's 1947 independence, and came at a time when relations with on-off ally the United States are fraying over alleged Pakistani support for militants waging war in Afghanistan.
Pakistani cricketing legend-turned-politician Imran Khan was elected head of the government on Friday when lawmakers in the lower house - the National Assembly - of parliament voted for a new prime minister.More news: Trump signs bill named for Sen. McCain, doesn’t mention him
Earlier this week, former Indian captain Kapil Dev said he will not be attending the oath-taking ceremony, citing "personal reasons".Dev was one of the three cricketers from India invited to attend Khan's swearing-in ceremony, along with Sidhu and Sunil Gavaskar. He congratulated the nation on election victory of Imran Khan as prime minister of Pakistan. "We will hold you accountable for stealing votes" firmly said Sharif and continued his diatribe over systematic election rigging hurling accusations. The army and Khan have denied the claims.
The PPP and PML-N have dominated Pakistani politics for decades, governing several times in between periods of military rule.
The party has already formed a government in its stronghold of Khyber Pakhtunkhwa province, and an alliance with regional parties in the southwestern province of Balochistan.
Murtaza Abbasi, a PMLN legislator, said in parliament that Mr Khan was "brought here by aliens", a euphemism for the military.
Most pressing will be a looming economic crisis, with speculation that Pakistan will have to seek a bailout from the International Monetary Fund.