His resignation comes less than a day after Brexit secretary David Davis stepped down
Boris Johnson has resigned as the British foreign secretary - another major ministerial resignation for Theresa May amid continuing political turmoil over Brexit.
In his resignation, the outgoing foreign secretary claimed the 'Brexit dream is dying', and said the UK risked becoming a 'colony' of the EU under current proposals.
The departure of Mr Johnson - who was one of the highest profile campaigners for the UK to leave the EU - follows Brexit Secretary David Davis’ resignation overnight.
Brexit junior minister Steve Baker has also resigned.
Mr Johnson will be replaced as foreign secretary by health secretary Jeremy Hunt, Downing Street confirmed on Monday evening.
The Queen has been pleased to approve the appointment of Rt Hon @Jeremy_Hunt as Secretary of State for Foreign and Commonwealth Affairs.— UK Prime Minister (@10DowningStreet) July 9, 2018
The resignations comes only days after Theresa May announced that her cabinet had reached an agreement on Brexit proposals - including a plan for an EU-UK free trade area - after an all-day summit at her country retreat at Chequers.
In his resignation letter, Mr Johnson wrote: "Brexit should be about opportunity and hope. It should be a chance to do things differently, to be more nimble and dynamic, and to maximise the particular advantages of the UK as an open, outward-looking global economy.
"The dream is dying, suffocated by needless self-doubt."
Voicing his concerns about the planned Brexit approach, Mr Johnson added: "Since I cannot in all conscience champion these proposals, I have sadly concluded that I must go."
He also suggested the UK is "truly headed for the status of colony" if it agrees to follow "huge amounts" of EU law.
I am proud to have served as Foreign Secretary. It is with sadness that I step down: here is my letter explaining why. pic.twitter.com/NZXzUZCjdF— Boris Johnson (@BorisJohnson) July 9, 2018
In a statement, a Downing Street spokesperson said: “This afternoon, the Prime Minister accepted the resignation of Boris Johnson as Foreign Secretary.
"His replacement will be announced shortly. The Prime Minister thanks Boris for his work.”
Speaking in the House of Commons, Mrs May said she wanted to recognise "the passion that the former foreign secretary demonstrated in promoting a global Britain to the world as we leave the European Union".
Mrs May was briefly drowned out by laughs and jeers from the opposition as she spoke about the recent resignations.
On the subject of her cabinet's Brexit proposals, she observed: "This is the Brexit that is in our national interest - it is the Brexit that will deliver on the democratic decision of the British people."
Labour leader Jeremy Corbyn, meanwhile, said: "How can anyone have faith in the prime minister getting a good deal with 27 European Union governments when she can't even broker a deal within her own cabinet?
"Far from strong and stable, there are ministers overboard and the ship is listing - all at the worst possible time."
He added: "For the good of this country and its people, the government needs to get its act together and do it quickly - and if it can't, make way for those who can."
Mr Johnson took over the role of foreign secretary just under two years ago.
Having initially been considered a frontrunner for the Conservative leadership in the wake of Brexit, he ultimately did not contest the leadership contest that ultimately saw Theresa May elected.
Dominic Raab - who was also a 'Leave' supporter - has already been announced as the new Brexit secretary, and will take over from Mr Davis as negotiations with the EU enter a critical phase ahead of a final deadline of October.
Earlier, Tánaiste Simon Coveney played down the significance of Mr Davis resigning.
He explained: "I think for some time now the British negotiation has been out of No 10 [Downing Street].
"The Prime Minister is the person who makes the final call in relation to Britain's positioning on Brexit. Our focus has to be to work with the Prime Minister, but in particular to work with the [Michel] Barnier taskforce now to seek and get a lot more detail on the British position."