Mumtaz Qadri was hanged early Monday at a jail in Rawalpindi, the city's deputy police commissioner said.
Qadri was found guilty of shooting and killing Punjab Gov. Salman Taseer in January 2011.
Thousands of the executed man's supporters took to the streets in cities across Pakistan as news of his death emerged, and security forces are on high alert for his funeral Tuesday, where large numbers of mourners are expected.
Murdered for opposition to blasphemy laws
Qadri was the governor's security guard and allegedly killed him because he spoke out against the country's controversial blasphemy law. The law makes insulting Islam a crime punishable by death.
When the governor spoke to CNN in 2010, two months before his death, he said he didn't want to abolish the law.
Rather, Taseer said he wanted it "changed in such a way that if you insult any prophet, no matter who he is, then that is a criminal offense. But certainly not punishable by death."
The day after the governor's death, Qadri went to court and supporters greeted him with a hero's welcome
. They even showered him with rose petals and put a garland around his neck.
Amnesty: Execution 'no way to ensure justice'
While lauding the government's stance against extremism, Amnesty International protested the execution, saying that the "taking of a life is no way to ensure justice for the murder of Salman Taseer," and called for the country to impose a moratorium on capital punishment.
"Salman Taseer was a brave voice for religious tolerance in Pakistan and his murderer should be brought to justice, but carrying out more killings is a deplorable way to honour Salman Taseer's life and message," Champa Patel, Amnesty International's South Asia Regional Office Director, said in a statement.
Pakistan has executed more than 300 people in just over 14 months, the human rights organization said.