A ballot will be held between 1800GMT and 2000GMT on Wednesday in a room at the House of Commons and an announcement made as soon as possible afterwards.
British Prime Minister Theresa May said she would fight a vote of no confidence in her leadership of the Conservative Party later on Wednesday with "everything I have got".
Speaking outside her Downing Street office, she said a change of leadership would put Britain's future at risk and jeopardise Brexit negotiations.
TRT World's Simon McGregor-Wood reports from London.
Lawmakers from the Conservative Party triggered a confidence vote in her leadership after Britain's planned divorce from the European Union was plunged into chaos.
With less than four months left until the United Kingdom is due to exit on March 29, the world's fifth largest economy was tipping towards crisis, opening up the prospect of a disorderly no-deal divorce or a reversal of Brexit through a referendum.
Graham Brady, the chairman of the party's so-called 1922 committee, said the threshold of 15% of the parliamentary Conservative Party seeking a confidence vote had been reached.
"The threshold of 15% of the parliamentary party seeking a vote of confidence in the leader of the Conservative Party has been exceeded," Brady said.
A ballot will be held between 1800GMT and 2000GMT on Wednesday in a room at the House of Commons and an announcement made as soon as possible afterwards, he said.
"The votes will be counted immediately afterwards and an announcement will be made a soon as possible in the evening," Brady said.
TRT World's Sarah Morice has more.
Brexit is Britain's most significant political and economic decision since World War Two though pro-Europeans fear it will divide the West as it grapples with the presidency of Donald Trump and growing assertiveness from Russia and China.
The ultimate outcome will shape Britain's $2.8 trillion economy, have far reaching consequences for the unity of the United Kingdom and determine whether London can keep its place as one of the top two global financial centres.
May could be toppled if 158 of her 315 lawmakers vote against her.
May, a 62-year-old vicar's daughter who voted to remain in the EU, won the top job in the turmoil that followed the 2016 EU referendum but promised to implement Brexit, while keeping close ties to the bloc, as a way to heal a divided nation.
But on Monday she abruptly pulled a parliamentary vote on her deal - which seeks to keep Britain closely aligned with the EU after its exit - in the face of a probable rout.
Her trade minister, Liam Fox, said the government might not even put it to a vote unless the EU gave further reassurances on the so-called Irish backstop.
German Chancellor Angela Merkel said the 27 other members of the bloc would not change the Brexit deal the EU has spent two years negotiating.
Brexit-supporting lawmakers in her party say May has betrayed the people's vote in negotiations, while opponents say she struck a deal that is the worst of all worlds - out of the EU but with no say over many rules it has to abide by.
"Theresa May’s plan would bring down the government if carried forward," lawmakers Jacob Rees-Mogg and Steve Baker said in a statement.
"But our party will rightly not tolerate it. Conservatives must now answer whether they wish to draw ever closer to an election under Mrs May’s leadership. In the national interest, she must go."
The EU's top court ruled on Monday that Britain could cancel its Article 50 notice to leave without permission from other members and without losing special privileges.