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.
BBC political editor Laura Kuenssberg said she understood Mr Johnson is resolute that Mr Hunt should not stay on at the Foreign Office.
However she added that Mr Hunt is firm that he won't accept anything less than his current role, or becoming home secretary, chancellor or deputy prime minister.
He would consider other moves a demotion, she said.
She added that Dominic Cummings, the former chief of the Vote Leave campaign, is expected to become a senior adviser to the new prime minister.
It is also confirmed that David Frost, a former ambassador and senior official at the Foreign Office, will be appointed as a key negotiator on Brexit.
After his victory, Mr Johnson said his priorities were to deliver Brexit, unite the country and defeat Labour leader Jeremy Corbyn.
He 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.
Source: BBC