His decision to quit comes in response to a slew of resignations from multiple ministers in his old Cabinet (he has already appointed a new one), Tory MPs, and junior aides as well.
By Monday, Johnson said in his speech, a timetable for his departure and a successor should be finalised by the committee of senior Conservative lawmakers.
Outgoing prime ministers usually stay in office until a new one is selected. Within the Conservative Party, how does that happen?
Before we explain that, it is important to note that the opposition Labour Party has stated that it will call a parliamentary no-confidence vote if the Conservative Party doesn't kick Johnson out immediately.
"His own party have finally concluded that he's unfit to be prime minister. If they don't get rid of him, then Labour will step up in the national interest and bring a vote of no confidence because we can't go on with this prime minister clinging on for months and months to come," Labour Party chief Keir Starmer's statement read.
Selection by Elimination
The first step in choosing a new prime minister from within the party is nomination. Many senior MPs put their names on the ballot to be elected as the leader of the party.
But their applications can only be eligible if eight of their colleagues, who are also MPs, support their candidature. There needs to be more than two MPs in the race at least.
After the candidates are finalised in this way, a secret ballot election process is initiated.
In the first round, the candidate who receives the least number of votes will be eliminated. This process continues until only two candidates are left, after which the party members make their final decision about their next leader.
The deadline for the same is set by the 1922 Committee.
Who All Are Expected To Participate?
Some of the names that are expected to come forward are:
Rishi Sunak, former chancellor of the Exchequer
Sajid Javid, former health secretary
Liz Truss, foreign secretary
Penny Mordaunt, minister of state for Trade Policy
Nadhim Zahawi, chancellor of the Exchequer
Jeremy Hunt, chair of the Health and Social Care Select Committee
Ben Wallace, secretary of state for Defence
Tom Tugendhat, chairman of the Foreign Affairs Committee
Suella Braverman, attorney general for England and Wales