PHOTO: AFP
Prime Minister David Cameron secured the strong mandate he had sought with 397 of MPs voting in favour and 223 against, a majority of 174, after over 10 hours of passionate and often angry debate.
The result in the House of Commons means that British planes could start bombing over Syria within hours. Foreign Secretary Philip Hammond said the first strikes could come as early as "tomorrow night".
Earlier, Cameron kicked off the debate by urging MPs to "answer the call" from allies like France and the US, adding that bombing the "mediaeval monsters" of IS was "the right thing to do".
"The question is this: do we work with our allies to degrade and destroy this threat... or do we sit back and wait for them to attack us?" he said.
But many of the MPs crammed on to the Commons' benches and walkways spoke against air strikes while some 2,000 anti-war protesters held a second consecutive night of protest outside parliament.
"We need to stop bombing innocent countries," said one demonstrator, Theresa Gormley. "Thousands of innocent people will be killed by David Cameron and his friends."
Labour leader Jeremy Corbyn, who opposes military action, said Cameron's proposals "simply do not stack up".
"The spectre of Iraq, Afghanistan and Libya looms over this debate," Corbyn added, referring to unpopular British interventions in foreign conflicts over the last 15 years.
Asked when British air strikes on Syria could begin, Hammond told Channel 4 television: "Probably not tonight, but it could be tomorrow night".
Cameron has wanted to extend Britain's role in the fight against IS for months but made a fresh push which led to the vote after last month's Paris attacks which killed 130 people.
Britain already has eight Tornado fighter jets plus drones involved in the US-led coalition striking IS targets in Iraq.
However, it currently only conducts surveillance and intelligence missions over Syria.
The government is now set to deploy more jets and argues that the Royal Air Force's Brimstone missiles will be particularly valuable for precision strikes to avoid civilian casualties.
US Secretary of State John Kerry praised Cameron for bringing the vote to parliament Wednesday and urged all NATO countries to "step up support" for the fight against IS.
Military experts question how much difference Britain would make to the campaign, saying it may be more about wanting to stand shoulder-to-shoulder with allies like France and the United States.
Cameron again stressed that British ground forces will not be deployed to Syria as part of the action Wednesday, saying that would be a "mistake".
Labour was deeply divided on air strikes, with 67 of its 231 MPs reportedly voting in favour of air strikes, despite Corbyn opposing the move.
The party leader, who took office in September, let his party have a free vote on the issue because dozens of MPs, including his foreign and defence spokespeople, supported it.
In a highly unusual move, foreign affairs spokesman Hilary Benn closed the debate for Labour by speaking in favour of air strikes.
Benn drew rare and sustained applause from across the Commons, hours after Corbyn opened the debate for Labour by urging MPs to vote against strikes.
"We are here faced by fascists," Benn said, reminding his party that socialists had fought against Spanish dictator Francisco Franco in the 1930s.
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