Authorities said they had identified the mangled corpse of Belgian national Abdelhamid Abaaoud from fingerprints in the aftermath of Wednesday's raid and gun battle in which at least two people died including a female suicide bomber.
"The spider in the web is no longer a danger," Belgian Justice Minister Koen Geens said, calling it a "breakthrough".
The body had been found riddled with holes amid the wreckage in the aftermath of Wednesday's raid, Paris's prosecutor said in a statement. The prosecutor later added that it was unclear whether Abaaoud had detonated a suicide belt.
The Moroccan-born Belgian militant, 28, was accused of orchestrating last Friday's coordinated bombings and shootings in the French capital, which killed 129 people. Seven assailants died in the attack and a suspected eighth is still on the run.
French Prime Minister Manuel Valls broke the news of Abaaoud's death to parliament on Thursday to applause from French lawmakers who were voting to extend a state of emergency for three months.
"We know today ... that the mastermind of the attacks - or one of them, let's remain cautious - was among those dead," Valls told reporters.
PROMINENT RECRUITER
Even before last week's attacks, Abaaoud was one of Islamic State's highest-profile European recruits, prominently profiled in the group's slick online English-language magazine Dabiq, where he boasted of crossing European borders to stage attacks.
The group, which controls swathes of Iraq and Syria, has attracted thousands of young Europeans, and Abaaoud was seen as a leading figure in luring others to join, particularly from his home country Belgium.
He claimed to have escaped a continent-wide manhunt after a police raid in Belgium in 2013 in which two other militants were killed. His own family has disowned him, accusing him of abducting his 13-year-old brother, who was later promoted on the Internet as Islamic State's youngest foreign fighter in Syria.
While quickly tracking him down will be seen as a major success for French authorities, his presence in Paris will focus more attention on the difficulty European security services have in monitoring the continent's borders.
Before the attacks, European governments thought Abaaoud was still in Syria. "This is a major failing," said Roland Jaquard at the International Observatory for Terrorism.
French officials have called for changes to the functioning of the EU's Schengen border-free travel zone, which normally does not monitor the entry and exit of citizens of its 26 countries. Hundreds of thousands of people have reached Europe as Syrian refugees in recent months, including at least one person using a passport found at the scene of Friday's attacks.
Lawmakers in the French National Assembly voted to extend the state of emergency for three months by 551 votes to six. The state of emergency allows police to search homes without a judicial warrant and impose house arrest on suspects, among other measures.
"FACED WITH BARBARISM"
"This is the fast response of a democracy faced with barbarism. This is the effective legal response in the face of an ideology of chaos," Valls told parliament.
Neighbouring Belgium, stung by revelations that several of the attackers were based there, announced a 400 million euro (£280.39 million) security crackdown. Prime Minister Charles Michel announced plans for new laws to jail jihadis returning from Syria, shut unregistered mosques, expel hate preachers and ban anonymous purchases of mobile phone cards.
Heavily armed French police swooped on the house where Abaaoud was holed up in the Paris suburb of St. Denis on Wednesday before dawn, triggering a huge firefight and multiple explosions.
Officials had said on Wednesday that two people were killed in the raid, including a female suicide bomber. Forensic scientists were trying to determine whether a third person had died. Eight people were arrested.
French police sources say the St. Denis cell had been planning a new attack on Paris's La Defense business district.
The victims of the deadliest attacks in France since World War Two came from 17 different countries, many of them young people out on a Friday night at bars, restaurants, a concert hall and a soccer stadium. Islamic State says it carried out the attacks in retaliation for French air raids on its positions.
France has called for a global coalition to defeat the group and has launched air strikes on Raqqa, the de-facto Islamic State capital in northern Syria, since the weekend. Russia has also targeted the city in retribution for the downing of a Russian airliner last month that killed 224.
The attacks could bring common cause between Western capitals and Moscow, more than a year after the United States and European Union imposed financial sanctions on Russia over its annexation of territory from Ukraine.
Russia and the West are divided over Syria, with Moscow supporting President Bashar al-Assad and Western countries saying he must leave power to end a 4-year-old civil war. Moscow launched air strikes in Syria six weeks ago and says it is targeting Islamic State, although most of its strikes have hit areas controlled by other groups opposed to Assad.
There are signs that the recognition of a common threat since the Paris shootings and the Russian air crash could prompt more efforts to cooperate.
RUSSIA'S ROLE
European Commission chief Jean-Claude Juncker wrote to President Vladimir Putin this week, suggesting closer trade ties between the 28-nation EU and a Russian-led economic bloc, linking them to progress on implementing a ceasefire in Ukraine.
In the letter, seen by Reuters, Juncker underlined the importance of good relations between the European Union and Moscow, "which to my regret have not been able to develop over the past year". He said he had asked Commission officials to study options for closer ties between the EU and the Moscow-led Eurasian Economic Union of former Soviet states.
French President Francois Hollande is due to meet Putin in Moscow on Nov. 26 to discuss how their countries' militaries might work together.
Two days before that, Hollande will meet U.S. President Barack Obama in Washington to discuss the role of a U.S.-led coalition in any unified effort against Islamic State.
France is one of several European countries participating in the U.S.-led Operation Inherent Resolve strikes against Islamic State targets in Iraq, and two months ago became the only European country to join U.S.-led strikes in Syria as well.
Obama on Thursday reiterated the U.S. position that eradicating the group was tied up with ending the civil war in Syria, which could not happen as long as Assad was in power.
"Bottom line is, I do not foresee a situation in which we can end the civil war in Syria while Assad remains in power," he told reporters in Manila on the sidelines of the annual Asia-Pacific Economic Cooperation (APEC) summit.
