More than two-thirds of the members of the House of Commons opposed Brexit, and in the weeks after June's shock referendum vote, many people outside parliament hoped that MPs could stop it from happening.
But pro-Europeans in Prime Minister Theresa May's own Conservative party and among the Labour opposition were gradually forced to accept defeat, and said they would vote against deeply held beliefs.
Their dilemma was laid bare in two days of debate this week on a bill empowering May to start the process, as MPs stood up one after another to explain why they would back her despite their fears for the future.
"I lost the case. I made it with passion, I sacrificed my position in government for it," said former Conservative finance minister George Osborne, one of the strongest campaigners against Brexit.
"In the end we have to now accept that in a democracy the majority has spoken."
Fellow MP Anna Soubry, who like Osborne has warned of the risks of leaving Europe's single market, said it was a "great folly" but agreed to back the bill.
"How on earth did we ever come to put to the people an alternative that we then said would make them worse off and less safe and would weaken our nation?" she said.
She added: "History will not be kind to this parliament."
'Potentially catastrophic'
Labour leader Jeremy Corbyn ordered his MPs to support the bill in a preliminary vote on Wednesday, to reflect the fact that two-thirds of them represent constituencies that voted to leave the EU.
But his spokesman, Keir Starmer, one of a majority of Labour lawmakers who opposed Brexit, struggled through his Commons speech endorsing the bill.
Heckled by Tory MPs, he asked them to be "courteous" in accepting the deep divisions in his "fiercely internationalist" party over the policy.
Former minister Margaret Beckett said she too would fall into line, but said "I fear that its consequences, both for our economy and our society, are potentially catastrophic".
Dozens of Labour lawmakers rebelled, however, including Ian Murray, Labour's only MP in Scotland, who said he did so with a "heavy heart".
"I will do so in the knowledge that I can walk down the streets of Edinburgh South and look at my constituents in the eye, and say to them I've done everything I possibly can to protect their jobs, livelihoods and the future for their family," he said.
The bill was approved on Wednesday evening by a vote of 498 to 114, and will receive its final vote in the Commons next week, before heading to the upper House of Lords.
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'Crossing its fingers'
The MPs' turmoil was in stark contrast to the jubilation of those who have spent years in the political backwaters for their euroscepticism.
"Tonight there will be an historic vote in this place, a vote that I never thought I would see in my political lifetime," Conservative MP Peter Bone said.
His colleague Jacob Rees-Mogg had earlier hailed "that noble, brave, glorious decision the people made on that day of legend and song, June 23".
But Conservative former minister Ken Clarke, a committed europhile, poured scorn on pro-Brexit campaigners and accused them of pursuing a fantasy "wonderland".
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Sarah Olney, of the pro-European Liberal Democrats, told parliament: "We are effectively being asked to jump out of an aeroplane, without knowing whether or not we are securely attached to a parachute".
And Angus Brendan MacNeil of the Scottish National Party (SNP), which opposes Brexit, warned: "People assume the House of Commons knows what it's doing. It doesn't.
"It's crossing its fingers and hoping for the best."
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