The two candidates have spent the past month touring the UK in the hopes of winning the votes of Conservative party members. Now, the vote is over and the new prime minister will be declared shortly.
But what time will the new prime minister be announced and how will it happen?
When will the new prime minister be announced?
The result is due to be announced on Monday, September 5, at 12.30pm, in Westminster, in front of MPs and peers.
Chairman of the 1922 Committee of backbench MPs, Sir Graham Brady, will announce the result of the contest.
How can I watch live?
You can follow the Standard’s live blog of the announcement.
Alternatively, the result will be shown live on BBC News and Sky News.
What was the voting process?
The voting process was in two stages.
In stage one, Conservative MPs chose two candidates to put forward to stage two. This took place through a series of votes, and is how the field was narrowed down to Truss and Sunak. Those who were eliminated from the contest during this stage were:
In stage two, the two MPs selected faced a ballot of Conservative Party members, with each member voting only once.
Ballots were sent to members via post between August 1 and August 5. The vote closed at 5pm on Friday, September 2.
The candidate who receives the most votes will become the next prime minister.
When will Boris Johnson leave office?
Here he will submit his resignation and the Queen will formally dismiss him from his role.
Outgoing prime ministers typically make a speech from outside Number 10 Downing Street before submitting their resignation.
When will the new prime minister be appointed?
The Queen will appoint the new prime minister from Scotland for the first time, the Palace confirmed, breaking the tradition of appointing the new leader from Buckingham Palace.
She will formally appoint the new leader on Tuesday, September 6, after dismissing Mr Johnson. The new prime minsiter typically makes a speech outside Number 10 Downing Street, but as they will be appointed at Balmoral, they may make their speech from Scotland instead.
From Tuesday afternoon, it is expected that the new leader will begin to appoint their top government team.
When could there be another general election?
The maximum term for Parliament is five years. As the current Parliament first met on December 17, 2019, it will be automatically dissolved on December 17, 2024. This means that the next general election is set for January 2025.
However, both Theresa May and Boris Johnson called early elections in an attempt to solidify their leadership. Therefore, it is possible that the new prime minister could call an early election to try to do the same.