Prime Minister Stephen Harper's Conservatives, wielding a majority in the House of Commons, pushed through a motion on enlarging the mission in a vote 142 to 129, despite opposition parties' vigorous objections.
“Our Government believes that we must act to protect Canadians against the threat of terrorism at home and abroad," he said.
Canada first joined the US-led airstrikes on the IS group in November.
Its expanded air campaign was authorized until March 30, 2016.
Harper has defended the need for sorties into Syria, saying the IS group "must cease to have any safe haven in Syria."
He pointed to its movement of heavy equipment across the Iraqi border into Syria.
The prime minister also noted that IS fighters have threatened Canada in propaganda videos.
“As a result of ISIL’s specific threats against Canada and Canadians, our Government has worked closely for the past six months as part of a broad international Coalition, including our closest allies, to help degrade and disrupt ISIL’s ability to inflict harm.
At least six Canadians have died over the last two years fighting alongside extremists in Syria and Iraq.
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In the aftermath of two jihadist-inspired attacks in Ottawa and rural Quebec last October, a majority of Canadians have told pollsters they support the military mission against the IS group.
Opposition parties, however, warned that airstrikes against the IS group in Syria may implicitly aid Syrian President Bashar al-Assad, and embroil Canada in a regional conflict that could drag on for decades.
New Democratic Party Leader Thomas Mulcair decried the move "expanding a misguided war in Iraq to a dangerous new phase in Syria."
"This is simply not Canada's war to fight," he said.
Canadian airstrikes in Syria are not authorized by the United Nations, nor is it a NATO mission.
Canada has also deployed about 70 special forces soldiers to train Kurds in northern Iraq.
They came under mortar and machine gun fire while training Iraqi troops near the frontlines in mid-January, and a Canadian soldier was killed by friendly fire on March 6.
Harper said that militarily, the “mission will remain focused on targeting ISIL from the air and advising and assisting Iraqi Forces to fight ISIL more effectively on the ground."