Supporters consider Qadri a defender of Islam for killing popular Punjab governor Salman Taseer - for whom he served as a bodyguard.
Hundreds of hardline Muslim activists in Pakistan set fires near parliament and clashed with police on Sunday to protest the execution of a man they consider a hero for assassinating a governor over his criticism of harsh blasphemy laws.
Police fired tear gas at the protesters, who had gathered about 700 metres from the parliament building in Islamabad, the capital, footage on local Geo TV showed.
The outpouring of support for executed ex-bodyguard Mumtaz Qadri highlights the growing tension between hardline Islamist groups and Pakistan's civilian government, which has vowed to crack down on extremism.
More than 60 people, the majority of them police officers, were injured in the clashes on Sunday, hospital officials told Reuters.
"They are all minor injuries, like being hit by stones," said Dr Aisha Issani, spokesperson for the PIMS hospital in Islamabad.
By mid-evening on Sunday, the military was called in to secure the situation.
"Army has been requisitioned by the Govt to control situation and secure Red Zone," military spokesman Gen. Asim Bajwa tweeted on his official account, referring to the area around the parliament.
Supporters consider Qadri a defender of Islam for killing popular Punjab governor Salman Taseer - for whom he served as a bodyguard - because Taseer had criticized a Pakistani law that mandates the death penalty for insulting Islam or the Prophet Mohammad.
Taseer had raised questions about the law - which is harsher in Pakistan than in most Muslim countries - as part of his support of a Christian woman he said was unjustly charged with the crime.
Last year, 210 cases of criminal blasphemy were filed. Critics say many cases are levelled against Christians and other religious minorities and are often used to exact revenge or seek advantage in personal or business disputes.
At least 65 people, including lawyers, defendants and judges, have been murdered over blasphemy allegations since 1990, according to figures from a Center for Research and Security Studies report and local media.