Mr Johnson is facing a vote of no confidence by Tory MPs amid anger across the party at the disclosures over lockdown parties in Downing Street.
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.
It comes after 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.
In order to oust the Prime Minister, the rebels will need 180 MPs – and allies of Mr Johnson made clear he is determined to fight to stay on.
Sir Graham Brady said in a statement: “The threshold of 15 percent of the parliamentary party seeking a vote of confidence in the leader of the Conservative Party has been exceeded.
“In accordance with the rules, a ballot will be held between 1800 and 2000 today Monday June 6 — details to be confirmed.
“The votes will be counted immediately afterwards.
"An announcement will be made at a time to be advised. Arrangements for the announcement will be released later today.”
Almost 30 Tory MPs have publicly urged the Prime Minister to resign amid the fallout from revelations about Downing Street parties held during lockdown.
But Health Secretary Sajid Javid stuck by the PM, adding: “If there is (a vote) the Prime Minister will stand and fight his corner with a very, very strong case.”
Sir Graham said he had informed Mr Johnson on Sunday that the threshold of 15 percent of the parliamentary party calling for a vote had been passed.
He said: “I have followed the rules that we have in place. I notified the Prime Minister yesterday and we agreed the timetable for the confidence vote to take place.
“He shared my view, which is also in line with the rules that we have in place, that that vote should happen as soon as it could reasonably take place and that would be today.”
A No 10 spokeswoman said: “Tonight is a chance to end months of speculation and allow the Government to draw a line and move on, delivering on the people’s priorities.
“The PM welcomes the opportunity to make his case to MPs and will remind them that when they’re united and focused on the issues that matter to voters there is no more formidable political force.”
Foreign Secretary Liz Truss tweeted: “The Prime Minister has my 100 percent backing in today’s vote and I strongly encourage colleagues to support him.
“He has delivered on Covid recovery and supporting Ukraine in the face of Russian aggression.
"He has apologised for mistakes made. We must now focus on economic growth.”
Sir Graham Brady speaking today
POOL
Prime Minister Boris Johnson
Victoria Jones