Boris Johnson will head to Downing Street later after taking over from Theresa May as prime minister.
The new Conservative leader will take office on Wednesday afternoon following an audience with the Queen at Buckingham Palace.
After entering Downing Street, he is expected to announce a clutch of senior cabinet posts, including chancellor of the exchequer and home secretary.
Sources close to Mr Johnson say his top team will reflect “modern Britain”.
He is expected to use the opportunity to increase the number of women in full cabinet positions and boost the representation of ethnic minorities.
Mr Johnson won a decisive victory over Foreign Secretary Jeremy Hunt in a ballot of Tory members – gaining a 66.4% total share of the vote.
Conversations are said to be “ongoing” between Mr Hunt and Mr Johnson about the foreign secretary’s next role.
After his victory, Mr Johnson said his priorities were to deliver Brexit, unite the country and defeat Labour leader Jeremy Corbyn.
The ex-mayor of London is expected to address the nation for the first time outside Downing Street at about 16:00 BST after accepting the Queen’s invitation to form a government.
That will follow Theresa May formally giving her resignation as prime minister at Buckingham Palace.
Wednesday 12:00 BST onwards: Theresa May takes part in her last Prime Minister’s Questions. After lunch she will make a short farewell speech outside No 10 before travelling to see the Queen to resign.
Boris Johnson will then arrive for an audience at Buckingham Palace where he will be invited to form a government.
After that he will make a speech in Downing Street before entering the building for the first time as prime minister.
Later, he will begin announcing his most senior cabinet appointments, such as chancellor, home secretary and foreign secretary, and will make and take his first calls from other world leaders.
Thursday: Mr Johnson is expected to make a statement to Parliament about his Brexit strategy and take questions from MPs. Parliament will break up for its summer recess later.
The new PM will also continue announcing his new cabinet.