A result is expected at around 9pm, after two hours of voting.
Mr Johnson earlier pleaded with Tory MPs to back his leadership rather than indulge in “pointless” internal warfare as he faced a crunch vote on his political future.
The Prime Minister wrote to Tory MPs and addressed them at a private meeting in Westminster two hours before voting began.
He reminded Conservatives that “under my leadership” the party had won its biggest electoral victory in 40 years.
He warned them that Tory splits risk the “utter disaster” of Sir Keir Starmer’s Labour entering Downing Street, propped up by the SNP.
According to briefed extracts from his speech, he said: “The only way we will let that happen is if we were so foolish as to descend into some pointless fratricidal debate about the future of our party."
In his separate letter to Conservatives, Mr Johnson said: “Tonight we have the chance to end weeks of media speculation and take this country forward, immediately, as one united party.”
It is an opportunity to “draw a line” under the issue, he added.
The PM continued: “I do not believe our voters will lightly forgive us if – just when they need us most to be focusing on them – we appear once again to be focusing on Westminster politics."
Mr Johnson was informed early on Sunday afternoon that he would face the vote after more than 15 percent of the party’s MPs – 54 parliamentarians – had submitted formal letters, emails or messages saying they had lost confidence in him.
Sir Graham Brady, chairman of the backbench 1922 Committee, confirmed in a statement that he has now received the 54 letters from Conservative MPs needed to trigger a vote.
The vote – by secret ballot – will take place at Westminster on Monday between 6pm and 8pm, with the count to take place immediately afterwards.
A steady stream of Tory MPs called publicly for the Prime Minister to stand down in the wake of Sue Gray’s report into breaches of the Covid regulations in No 10 and Whitehall.
But Tory concerns go far wider, covering the Prime Minister’s policies which have seen the tax burden reach the highest in 70 years and concerns about his approach to ethics and cultural issues.
To oust the Prime Minister, however, the rebels need 180 MPs, and allies of Mr Johnson made clear he is determined to fight to stay on.
Prime Minister Boris Johnson
Alberto Pezzali
Sir Graham Brady announced the ballot today
POOL
