At least three gunmen reportedly rammed their cars into the minister's vehicle, stepped out and shot him at point-blank range. Gemayel, 34, was rushed to the hospital where he later died of his wounds.
Gemayel, elected to parliament in 2000 and again in 2005, is the third Lebanese anti-Syrian figure to be assassinated since former Prime Minister Rafik Hariri's killing in February 2005. He was a member of the Christian Phalange Party, which controlled one of the largest militias fighting in the 1975-1990 Lebanese civil war.
Gemayel's death has caused uproar in Lebanon and it threatens to heighten tensions between the anti-Syrian majority and pro-Damascus opposition lead by Hezbollah, which is determined to topple the government. Hundreds of supporters gathered outside the hospital Gemayel was rushed to and shouted slogans against Syria. In the Christian town of Zahle in eastern Lebanon, protestors blocked off streets and shouted anti-Hezbollah sentiments.
Gemayel's father, still prominent in political and Christian circles, urged supporters to avoid retribution and instead appreciate his son's martyrdom to preserve his cause to protect Lebanon.
Syria has officially condemned the killing as has Hezbollah, which called for an investigation.
U.S. Undersecretary of State Nicholas Burns said it was a "sad day for Lebanon." He told Reuters that "[The United States] is shocked by this assassination" and that it is viewed as an act of terrorism and intimidation.
At the United Nations, the Security Council unanimously adopted a resolution condemning the attack.
"The Security Council condemns any attempt to destabilize Lebanon through political assassination or other terrorist acts," the statement said, adding that Gemayel was "a patriot who was a symbol of freedom and of the political independence of Lebanon."
But it is unclear exactly who is responsible for the killing. Daniel Byman, a senior fellow at the Saban Center for Middle East Policy at the Brookings Institute, said anyone could have done it.
"Things have always been very murky in Lebanese politics and there are a lot of different agendas going on in Lebanon at the same time," he said.
With Gemayel's death, the resignation of or death of two more cabinet ministers could bring down Lebanese Prime Minister Fouad Siniora's government. He is asserting legitimacy of his government despite the resignation of six-pro-Syrian ministers earlier this month. According to Byman, "the threat to Siniora's government is very real. ... Siniora's government was embarrassed by its inability to stop the violence in the clashes between Hezbollah and Israel in July 2006. Especially after this assassination, people will now turn to their own communities for support rather than to the government."
Pro-Syrian Hezbollah and its allies accuse Siniora's government of being allied with the United States. With the resignation of the six Hezbollah-allied cabinet ministers, Hezbollah is arguing that Siniora's government no longer represents Shiite Muslims.