New Prime Minister Theresa May has made Boris Johnson, the former London mayor who led the Brexit campaign, foreign secretary in her new government.
He replaces Philip Hammond, who becomes chancellor. Ex-Energy Secretary Amber Rudd is home secretary and Eurosceptic David Davis is the Brexit secretary.
Ex-chancellor George Osborne was fired, the BBC's Laura Kuenssberg said.
On arriving at Downing Street, Mrs May vowed to lead a government that works for all, not just the "privileged few".
The UK's second female prime minister promised to give people who were "just managing" and "working around the clock" more control over their lives.
Downing Street said she took a number of "congratulatory phone calls" from other European leaders on Wednesday evening, where she told them "some time" would be needed to prepare for EU exit talks.
In her appointments announced so far, Michael Fallon continues as defence secretary, and Liam Fox, who resigned as defence secretary in 2011, has a new role as secretary of state for international trade.
Theresa May's new cabinet appointments
- Chancellor - Philip Hammond
- Home Secretary - Amber Rudd
- Foreign Secretary - Boris Johnson
- Defence Secretary - Michael Fallon
- Secretary of State for exiting the European Union - David Davis
- International Trade Secretary - Liam Fox
Mrs May has spoken of the need to reunite the Conservative Party after the EU referendum, in which she backed a Remain vote.
Her new line-up includes big jobs for prominent Leave campaigners Mr Johnson - who was initially tipped as the next prime minister after the Brexit vote - Mr Fox, and Mr Davis, whose job title is "secretary of state for exiting the European Union".
UKIP leader Nigel Farage tweeted that the appointments of Mr Fox and Mr Davis were "inspired choices", adding: "I feel more optimistic now."
On Twitter, Mr Osborne, who was chancellor throughout Mr Cameron's tenure, said the job had been a "privilege", adding: "Others will judge - I hope I've left the economy in a better state than I found it."
The BBC's political editor Laura Kuenssberg said Mr Osborne had been "told his services were no longer required" because his "brand" was seen as "too tarnished".
Mr Johnson said he was "very humbled" to be appointed foreign secretary.
He said Mrs May had made a "wonderful speech" earlier, saying there was a "massive opportunity in this country to make a great success of our new relationship with Europe and with the world".
But Lib Dem leader Tim Farron predicted Mr Johnson would "spend more time apologising to nations he's offended" than working as foreign secretary.
The new prime minister had spoken by phone to German Chancellor Angela Merkel, French President Francois Hollande and Irish Taoiseach Enda Kenny, Downing Street said late on Wednesday.
A Number 10 spokeswoman said the PM had "emphasised her commitment to delivering the will of the British people to leave the European Union".
She added: "The prime minister explained that we would need some time to prepare for these negotiations and spoke of her hope that these could be conducted in a constructive and positive spirit."
By Laura Kuenssberg, BBC political editor
The biggest surprise is the appointment of Boris Johnson, the Tory members' darling, as the foreign secretary - one of the greatest offices of state, with a hugely different role as the UK contemplates life outside the EU.
There will be arguments in the coming days of course about how that role will compare and possibly pull against the newly-created "minister for Brexit", a role that's been filled by arch Eurosceptic David Davis, a serial campaigner for civil liberties who is difficult to placate. The Eurosceptic Liam Fox is in charge of drumming up trade.
But the decision that marks the clearest break with the past is the sacking of George Osborne, David Cameron's fixer and political friend for so long.
Earlier, after returning from Buckingham Palace, where she was formally appointed as prime minister by the Queen, Mrs May made a speech from outside 10 Downing Street.
Her husband Philip was standing behind her as she highlighted the "precious bond" between England, Scotland, Wales and Northern Ireland and between "every one of us".
"That means fighting against the burning injustice that if you're born poor you will die on average nine years earlier than others," Mrs May said.
For an "ordinary working class family", she added, "life is much harder than many people in Westminster realise".
"When it comes to opportunity, we won't entrench the advantages of the fortunate few, we will do everything we can to help anybody, whatever your background, to go as far as your talents will take you," Mrs May said.
Mrs May also paid tribute to her predecessor, David Cameron, saying he had been "a great modern prime minister".
Mr Cameron earlier gave his final speech as prime minister, saying it had been "the greatest honour" of his life and that the UK was "much stronger" than when he took over.