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 Labor 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.
Mr Johnson will inherit a wafer-thin parliamentary majority and, like his predecessor, will continue to rely on the support of the Democratic Unionists of Northern Ireland to govern.
Labor, the Lib Dems and the SNP have said they will oppose Mr Johnson over Brexit, although they have stopped short of threatening an immediate vote of no confidence.
The BBC’s political editor Laura Kuenssberg said Mr Johnson’s choice of his top team would be critical in his efforts to bring the warring factions of his party together.