The Commons decks have been cleared for a 10 hour-plus debate on the case for deploying RAF jets against jihadist targets before a crunch vote at around 10pm.
Bombing missions are likely to begin within days if the House delivers what the Prime Minister hopes will be a comfortable majority in favour, thanks to the support of dozens of Labour MPs.
He called the vote after Mr Corbyn failed to win support for his anti-war stance in a shadow cabinet riven by bitter divides over the party's direction and granted Opposition MPs a free vote.
Up to 50 - including shadow foreign secretary Hilary Benn - are expected to back strikes despite a furious backlash from anti-war campaigners who mounted a noisy protest outside Parliament and Labour HQ.
Democratic Unionists and the Liberal Democrats are also backing air strikes, outweighing the voices of around a dozen Conservatives defying the party line to oppose action.
But critics of the policy - including the 54-strong Scottish National Party - have been emboldened by criticism of the PM's case from an influential committee and controversy over his claims about the numbers of moderate Syrian forces.
Mr Cameron set out his strategy as a direct response to a highly-critical assessment by the foreign affairs select committee but it voted by four to three that he "has not adequately addressed concerns" in key areas.
At least 110 MPs from six different parties have signed up to an amendment seeking to block air strikes - spearheaded by Tory FAC member John Baron and the SNP's Westminster leader Angus Robertson.
SNP foreign affairs spokesman Alex Salmond said he believed the Government was engaged in a desperate "dash to bombing" because it feared the tide of opinion was turning against it.
The majority would be "less than expected" he predicted - and did not entirely rule out a shock result if the lengthy debate swung wavering MPs against the PM's position.
Some have called for more details of the make-up of what Mr Cameron said in his case for strikes were 70,000 moderate opposition forces on the ground in Syria - amid concerns a significant number are extremists.
A Downing Street source said: "We will leave predictions to others.
"The PM believes there is a compelling case for action and we will make that case in the Commons."
Mr Corbyn insisted "more and more" Labour MPs were becoming sceptical about the proposals and said there was "no hiding place" for Labour MPs after he agreed to the free vote.
Any bombing would cause civilian casualties, he said.
"Is that actually going to help the political process or should we not be putting our efforts into a political settlement in Syria, supporting the Vienna process and what is going on with that? Surely that is a much more profitable way forward than this."
But prominent backbencher Dan Jarvis - who served multiple tours of Iraq and Afghanistan with the Parachute Regiment - invoked Labour leaders' support for joining the fight against Nazism in 1939 in declaring his support for air strikes.
"Labour has a tradition of standing for the national interest when our country is under threat," he wrote in the New Statesman magazine - challenging Mr Corbyn and other critics to present a credible alternative.
"When the War Cabinet met in 1939, it was m inisters from our party - Clement Attlee and Arthur Greenwood - that tipped the balance in favour of resisting Nazism.
"Isil are the fascists of our time. Our struggle against them will be more complex, but the basic judgment it demands of us is the same: the readiness to do what is necessary to keep the British people safe."
Liberal Democrat leader Tim Farron said five tests he set down to the Prime Minister as a condition of his party's support " have been met as best they can".
"I will therefore be asking my parliamentary colleagues to join me in the lobby to support this motion," he said after a meeting of the parliamentary party at Westminster.
The Lib Dems have eight MPs - the same number as the DUP.
"I believe it is right to support what is a measured, legal and broad-based international effort to tackle the evil regime that has contributed to the hundreds of thousands of desperate refugees, fleeing for their lives," he said.
"We cannot tackle the refugee crisis without working on a plan to end the civil war in Syria. Furthermore, I cannot look those people in the eye without saying that I have done all I can to destroy Isil, to support the Vienna peace process and an effective transition away from the Assad regime."
Mr Robertson demanded an apology from Mr Cameron over his remarks - made at a behind-closed-doors meeting of the Tory backbench 1922 Committee.
"Hope PM Cameron regrets these unacceptable comments, retracts them and apologises at the start of the Syria debate," he wrote on Twitter.
Labour MPs also expressed outrage - amid reports the comments had swayed some Labour MPs back towards voting against air strikes.
John Mann posted: " Cameron calls us terrorist sympathisers. I call him a thick ignorant Flashman.
"How dare he? Don't imagine his own MPs will be happy either."
Lyn Brown said: " Outrageous. Vast majority of MPs, whatever conclusion they come to, will have thought long and deep about decision."
Mr Cameron has previously accused the Labour leader of seeking to "inflict his security-threatening, terrorist-sympathising, Britain-hating ideology on the country we love".
A poll found public opinion moving against air strikes - with the proportion in favour dropping from 59% to 48%.
The YouGov survey for The Times showed those against rising from 20% to 31% with undecideds unchanged on 21%.
But Mr Corbyn's personal rating also slumped - with just 24% judging him to be performing well, down from 30% in a week.
Labour deputy leader Tom Watson - who says there is a "compelling" case for air-strikes - joined calls for an apology.
"David Cameron's comments trivialise the decision MPs have to make," he said.
"MPs from all parties are treating that decision with the seriousness it deserves. The Prime Minister should retract and apologise for these remarks, which are disrespectful to those MPs who have a different view to him."
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