Health Secretary Jeremy Hunt has been named as his replacement.
Health Secretary and pro-Remain MP Jeremy Hunt has been appointed as the UK's new foreign secretary after Boris Johnson resigned earlier on Monday.
Explaining his exit, Johnson released a scathing letter attacking the PM's approach to Brexit, saying "the dream is dying, suffocated by needless self-doubt".
"We appear to be heading for a semi-Brexit, with large parts of the economy still locked in the EU system, but with no control UK over that system," he added, hours after his resignation was announced on Monday.
Prime Minister Theresa May's office said his replacement will be named later today.
On Sunday, Brexit Secretary David Davis also resigned. Housing minister Dominic Raab was eventually named as his successor.
The walkouts come days after May announced she had secured Cabinet approval for the UK to negotiate a soft Brexit in talks with the European Union.
News of Johnson's exit emerged just 30 minutes before May was due to appear before MPs in Parliament to defend the agreement, which was made on Friday.
Brexiteer Davis cited the proposal as being the driving force behind his resignation. In a statement, he said he quit because the negotiation stance would give "too much away, too easily" to EU negotiators, who he feared would ask for more concessions.
The plan "will leave us in at best a weak negotiating position, and possibly an inescapable one", he added.
Later on Monday, European Parliament President Donald Tusk waded into the media spectacle, expressing hopes on Twitter that the idea of Brexit could leave with Johnson and Davis:
Johnson’s resignation marks the end of a turbulent two-year stint as foreign secretary, during which he faced numerous calls to resign after a series of gaffes threatened to damage Britain’s image abroad and put people’s livelihoods at risk.
Offhand comment leaves British mother facing sentence hike in Iran
A misleading comment made during a parliamentary committee meeting in November, in which Johnson said Nazanin Zaghari-Ratcliffe was “simply teaching people journalism” when she was convicted for spying on Tehran in 2016, prompted an Iranian court to warn the mother-of-one that her 5-year sentence may be doubled. Zaghari-Ratcliffe maintains that she was on holiday in Iran when she was detained.
The blunder angered Labour opposition leader Jeremy Corbyn and London Mayor Sadiq Khan, who led calls for Johnson to be sacked, while Zaghari-Ratcliffe’s employer, the Thomson Reuters Foundation, urged him to “correct the serious mistake”.
Libya’s ‘dead bodies’
Johnson enraged his own party’s backbenchers at a Conservative Party conference in October when he said Libyan city Sirte could become a world-class tourist destination like Dubai if they “clear the dead bodies away”.
Late Libyan leader Colonel Muammar Gaddafi was captured and killed there in 2011 after nationwide protests against his rule descended into a civil war.
Johnson dismissed the ensuing backlash as political point-scoring and refused to apologise.
Italian minister Carlo Calenda hit out at Johnson in November 2016 after the then-foreign secretary said Italy should back Britain’s bid to retain access to the single market after Brexit "because you don’t want to lose prosecco exports".
Recalling their stormy exchange, economic development minister Calenda told Bloomberg that Johnson told him: "I don’t want free movement of people but I want the single market.
"I said, 'no way.' He said, 'you’ll sell less prosecco.' I said, ‘OK, you’ll sell less fish and chips, but I’ll sell less prosecco to one country and you’ll sell less to 27 countries.’
“Putting things on this level is a bit insulting," he concluded.
Whitehall sources defended Johnson’s Prosecco remark at the time, saying they were made during a “constructive” conversation.