Mujahid Ali Khan made the demand during a debate on the budget in the lower house of parliament.
Khan was recently elected to the National Assembly from Mardan constituency in Khyber-Pakhtunkhwa province.
Arif Alvi, a senior leader of the Tehrik-e-Insaf and a confidant of Imran, claimed Khan had made the demand in his personal capacity and it had nothing to do with the party.
Qadri was among police guards assigned to protect Taseer when he gunned down the Governor outside a restaurant in Islamabad in January 2011.
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He publicly confessed to killing Taseer, saying he had killed the Governor for demanding changes in the controversial blasphemy law.
An anti-terrorism court convicted Qadri and gave him two death sentences for two counts of terrorism and murder.
However, lawyers publicly feted Qadri during his appearances in court and showered rose petals on him.
The judge who sentenced him to death had to go into hiding after his office was ransacked by lawyers.
Pakistanis took to social networking sites like Twitter to protest against Mujahid Ali Khan's defence of Qadri.
Shehrbano wrote in a tweet, "Mujahid Ali Khan demands release of Mumtaz Qadri - the man who killed my father @SalmaanTaseer - in the National Assembly", while Aamna tweeted that she hoped the Tehrik-e-Insaf would discipline its lawmaker.