They quit amid divisions in the government over Brexit.
In a letter on Monday, Mr Johnson said the prime minister was leading the United Kingdom into a "semi-Brexit" with the "status of a colony".
Boris's resignation letter is scathing.
If Davis's resignation rattled May, Johnson's shook the foundations of her government.
The Brexit "dream is dying, suffocated by needless self-doubt", he said in the letter, which he posted to Twitter.
Hours later UK Foreign Minister Boris Johnson resigned over the political crisis.
Johnson had previously served as mayor of London and a lawmaker. Even Johnson's allies stepped back from outright mutiny, with one telling Business Insider that his resignation had been about changing "the policy not the person [in charge]".
She looks set on facing down a rebellion in her Conservative Party, where hardline Brexit supporters are livid over her plans to negotiate "a free trade area for goods" with the EU.
She said she and the two departed ministers "do not agree about the best way of delivering our shared commitment to honoring the result of the referendum" in which voters opted to leave the EU. One described accepting European Union rules as "the ultimate betrayal".
The majority of MPs are in favour of preserving frictionless trade across the UK-EU border and the open border on the island of Ireland.
She added that Britain must be free to protect its leading position in the services sector, including finance, after it leaves the European Union.
J.K. Rowling, who has been known to make her feelings about Brexit pretty clear in the past, waded in on Monday.
May has been trying for months to solve internal issues within the ruling Conservatives about which course to take before Brexit takes effect on March 29, 2019. He also warned that Britain was "headed for the status of a colony" within the bloc.
On Monday, May defended Friday's deal, which would allow for some ties between Britain and the EU. The timetable looks increasingly optimistic.
Hunt said it was a moment to show that Britain remained a "strong, confident voice in the world". Highlighted in red in this graphic, they are (front row left to right) Michael Fallon, Amber Rudd, Damian Green, Boris Johnson, Justine Greening, David Davis.
In her Commons statement, May urged the European Union to take her proposal seriously.
The reshuffle is expected to continue as Mrs May attempts to stamp her authorities following the Chequers summit last Friday.
Matt Hancock has been promoted from the Culture department to Health Secretary as the premier digs in for an attritional battle with Eurosceptics.
Who will be the next Prime Minister if Theresa May loses a confidence vote?
Mrs May scrambled to fill the holes in Cabinet last night with a series of radical moves - shifting Jeremy Hunt to Foreign Secretary and Dominic Raab into the key Brexit Secretary role. "I'd have to do something I didn't believe in", he told the BBC. "This mess is all of the Prime Ministers own making", opposition Labour Party leader Jeremy Corbyn told lawmakers.
Under Conservative Party rules, a leadership race could be triggered if at least 48 of her MPs declared their support for one.
She took to the House of Commons today to detail her Brexit proposals amid the chaos.