So, who remains in the running and where do they stand on Brexit, the issue which is likely to be the deciding factor in the race to become the next prime minister?
Who is still in the running?
Prominent Brexiteer and former foreign secretary Mr Johnson has been a leading voice of opposition to Mrs May’s Brexit plan.
The Old Etonian was one of the key players in the 2017 Leave campaign and resigned from the Cabinet following the Chequers summit in July.
Moving forward on Brexit, he has committed to keeping the October 31 deadline even if that means leaving without a deal and said he would step up no-deal preparations.
He also said he would refuse to pay the promised £39 billion to the European Union unless better Brexit terms are on offer.
He was heavily tipped as a successor to Mr Cameron but ruled himself out of the 2016 leadership contest after Mr Gove made a last-minute bid for the top job, meaning the former mayor of London's support base was diminished.
Backers: James Brokenshire, Gavin Williamson, Steve Baker, James Cleverly
The Foreign Secretary, 52, identifies as a one-nation Conservative.
He campaigned for Remain in the 2016 referendum and would be a moderate candidate on Brexit in the leadership election.
He has said he would keep a no-deal Brexit on the table, but warned it could be “political suicide” for the Conservatives as Parliament would force a general election.
He has called for a big increase in defence spending after Britain leaves the EU to counter rising global threats and has suggested slashing corporation tax to Irish levels of 12.5% to attract investment.
What he’s said about drugs: Told The Times he had a “cannabis lassi”, a yoghurt-based drink, when he was backpacking through India in his youth.
Backers: Liam Fox, Greg Hands, Mark Field.
The Environment Secretary had a bruising experience in the last Tory leadership race but was seen as one of the favourites to replace Mrs May, owing largely to his Brexiteer credentials.
Unlike Mr Johnson, he has not ruled out seeking a further delay to Brexit – possibly for months beyond October 31 – if a deal is in reach, and warned pursuing a no-deal scenario could lead to a general election in which Jeremy Corbyn could enter Number 10.
He has set out a “pro-business economic plan” to take on Mr Corbyn’s “Marxist message” and said he would replace VAT after Brexit with a “lower, simpler” sales tax.
In June 2016, Mr Gove, who was campaign manager for Johnson’s drive to succeed David Cameron, withdrew his support on the morning Mr Johnson was due to declare and threw his own hat in the ring instead.
On his vision, he said: “If I am prime minister of this country I want to ensure it’s the best place in the world to live, learn, raise a family, achieve your potential and start and run a business.”
The Home Secretary hopes to renegotiate the Withdrawal Agreement to remove the Irish backstop but does not want a delay beyond October 31.
Mr Javid, 49, backed Remain in the referendum but has since positioned himself as a firm Leaver.
He has set out a plan to tackle the Irish border issue by spending hundreds of millions on a technological solution, saying the UK has a moral duty to pay for measures at the border in an effort to secure a breakthrough.
On Brexit, he has said: "We will not beat the Brexit Party by becoming the Brexit Party."
Mr Javid has put forward a number of policy proposals, including cutting the top rate of income tax and establishing a £100 billion fund to invest in the UK’s infrastructure.
He became the first home secretary from an ethnic minority background when he was appointed in April 2018.
What he’s said about drugs: Has denied ever taking drugs.
Backers: Ruth Davidson, Jeremy Wright, Chris Skidmore.
Who didn't make the final cut?
The International Development Secretary travelled around the country filming himself chatting to voters in a bid to raise his profile in the race, and his campaign steadily gathered momentum.
He was one of the first to express how split the party is, saying he could not serve in a government led by Boris Johnson because of his stance on a possible no-deal exit from the EU.
Speaking to ITV News after being eliminated, International Development Secretary Mr Stewart said the result was "disappointing", adding how his exit means a no deal exit is now a real option.
He said: "Now that I've left this race, I'm the only person in the race that was saying a no deal Brexit would be a bad idea, every other candidate has left no deal on the table."
He added: "Clearly, the majority of my colleagues in the House of Commons at the moment agree with them and not with me."
When asked by ITV News Political Correspondent Libby Wiener if he believed he had been the victim of "vote lending, which gave you a surge but has now eliminated you", Mr Stewart said "all sorts of things might be happening".
On Boris Johnson, he previously said he has "many skills" but would not call him a "unifying figure".
What he’s said about drugs: Has apologised for smoking opium at a wedding in Iran.
Backers: David Gauke, Ken Clarke, Nicholas Soames.
When he launched his campaign, the former Brexit secretary said he planned to "fight for a fairer deal on Brexit, a fairer deal for British workers and a fairer society where every child can fulfil their potential".
He wants Brussels to ditch the Irish backstop as part of a new agreement, but if the EU will not move on the issue, he will walk away without a deal on October 31 – and has not ruled out suspending Parliament to ensure that MPs cannot block the UK’s exit.
He has said: “We need to up our game, which means being less naive, and being absolutely resolute about our intention and our resolve to leave on October 31.
"It seems to me that I’m the only candidate in this race that is clear about that.”
What he’s said about drugs: Has admitted taking cannabis as a student.
Backers: David Davis, Nadhim Zahawi, Maria Miller.
Before dropping out of the race, the Health Secretary, 40, had said he would take a different approach to try to get Commons support for a Brexit deal rather than the tactics Mrs May used.
He told ITV News: "Bringing the country together is absolutely critical for the next leader, and, of course, the party.
"And to do that, we need to deliver Brexit but not be defined by Brexit."
He insisted a no-deal Brexit is not a credible option and Parliament would never allow it.
He set out a Brexit delivery plan to leave by October 31, including establishing an Irish border council, made up of UK and Irish officials, to prevent the return of a hard border and time-limiting the backstop.
He also pledged to scrap business rates for small retailers and increase a tax on internet companies to “level the playing field” for high streets, and has set out his vision for a foreign policy that boosts trade and “resists protectionism”, while also promising to “uphold our values”.
What he’s said about drugs: Is understood to have tried cannabis as a student but has not used drugs since university.
Backers: Damian Green, Tracey Crouch, Caroline Spelman.
The 55-year-old unsuccessfully ran for the leadership against Theresa May in the 2016 contest.
She quit the last contest after telling The Times having children gave her a "very real stake" in Britain's future - in contrast to Mrs May, who was denied motherhood for health reasons.
Mrs Leadsom, whose decision to quit as Leader of the House proved to be the final straw for Mrs May's premiership, has now also confirmed she is running once again.
She said she believed a "determined Brexiteer" could have taken Britain out of the EU by now.
She set out a plan to scrap the Withdrawal Agreement and instead “massively ramp up” preparations for a “managed” exit without a full deal.
Mrs Leadsom also promised to tackle climate change at home and abroad and establish a cross-party commission to find a solution to funding social care, and warned that bold tax-cutting pledges could easily be blocked by Parliament.
What she’s said about drugs: Told the Independent that she “smoked weed at university and have never smoked it again since”.
Backers: Chris Heaton-Harris, Heather Wheeler, Derek Thomas
"We've seen basically the same faces saying the same things that they've been saying for the last three years," Mr Harper told the Daily Telegraph when he announced he would like to be the next prime minister.
A former Remain supporter who now accepts the referendum result, Mr Harper called for a “short, focused” extension to allow for the deal to be renegotiated but said he would be prepared to leave with no deal if that is not possible.
He claimed sticking to an undeliverable October 31 exit date could risk making Nigel Farage even stronger.
What he’s said about drugs: Has denied taking any drugs.
Backers: William Wragg, Jackie Doyle-Price, Scott Mann.
Ms McVey said she would be prepared as leader to walk away without a Brexit deal come the deadline of October 31.
Ms McVey also launched Blue Collar Conservatism, which aims to target "working class voters".
At the launch of Blue Collar Conservatism, she said the next leader must be a "Brexiteer who believes in Brexit".
What she’s said about drugs: A spokesman told The Telegraph she “has never taken cocaine and never would”. But she has said she has smoked cannabis in the past.
Who left the race before it really started?
As the only contender open to a second referendum, the former universities minister was widely seen as a rank outsider.
His five-point plan would've given MPs a “final chance” to get a Brexit deal through Parliament while also preparing for a referendum if that failed.
The public would have been offered a binding choice between a no-deal Brexit, a revised deal or remaining in the EU.
Key quote: “The world won’t wait for Westminster, no matter how loudly we shout, and no matter how damaging a prolonged Brexit process is for Britain.”
What he’s said about drugs: Has denied taking any drugs.
Backers: Dominic Grieve, Guto Bebb, Phillip Lee
James Cleverly had stood for leadership of the party but decided to drop out of the race, claiming he did not believe he would have enough backing to justify standing.
Housing Minister Kit Malthouse, who is widely credited as the convener of both Conservative Leavers and Remainers to develop a compromise on Mrs May's withdrawal agreement, said there was a "yearning for change", yet later withdrew from the race as well.
So what happens with Brexit?
The next Conservative leader could have a huge influence over the direction Brexit ends up taking, especially if Mrs May's Withdrawal Agreement Bill is rejected by Parliament.
Mrs May's successor could be heavily influenced by hard-line Brexiteers in the Commons, who have been highly critical of Mrs May's approach to the leaving the EU.