As the June 8 poll ended in a hung parliament, with no party holding an absolute majority in the House of Commons, Mrs May pledged the Tories would offer "stability" as the largest party with the most votes.
Election 2017: So what happens now with a hung parliament?General Election 2017: Live news & reaction in Yorkshire and across UKFind friends and understand Facebook: Advice for new MPs‘Greatest privilege’: Nick Cleggs’ 12 years in Sheffield Hallam comes to an endJames Reed: Theresa May’s reputation in tatters after election gamble failsThey said what? Through the night of the 2017 General Election in quotesBut Conservative former minister Anna Soubry said she should "consider her position" and take personal responsibility for a "dreadful" campaign and a "deeply flawed" manifesto after choosing to go to the country three years early in the hope of extending her majority.
Labour leader Jeremy Corbyn called on the Prime Minister to resign, saying she should "go and make way for a government that is truly representative of this country".
But Tory sources indicated she would continue in Number 10.
"Certainly that's what's expected," a source said.
But former chancellor George Osborne, sacked from the Cabinet by Mrs May and now editor of the Evening Standard, told ITV: "Clearly if she's got a worse result than two years ago and is almost unable to form a government then she I doubt will survive in the long term as Conservative party leader."
With 646 out of 650 constituencies declared, the Tories had 315 seats, Labour 261, the SNP 35 and the Liberal Democrats 12.
The Democratic Unionist Party, which increased its representation at Westminster from eight to 10, signalled it was ready to discuss working with the Tories on issues such as Brexit and keeping the UK together.
With the party in a position to hold the balance of power at Westminster, senior MP Sir Jeffrey Donaldson said the DUP would be "serious players" in the hung parliament, telling the BBC: "This is perfect territory for the DUP because obviously if the Conservatives are just short of an overall majority it puts us in a very strong negotiating position and certainly that is one we would take up with relish."
After 646 results, Mrs May's party had 42.4% of the vote while Labour's share had increased by almost 10 points from its 2015 level to 40.08%.
It was mathematically impossible for the Tories to secure the 326 seats needed for an outright majority, but with the support of the DUP - and the assumption that Sinn Fein will not take up the seven seats won by the party - Mrs May could try to soldier on with a minority administration.
The pound plummeted as the shock figures set the scene for political turmoil at Westminster, disruption to upcoming Brexit negotiations and the possibility of a second election later in the year.
The night was marked by a collapse in Ukip support and a rash of high-profile losses for the SNP, as British politics returned to a two-party system on the greatest scale since the 1970s.
The Tories lost eight frontbenchers, with ministers Jane Ellison, Simon Kirby, Gavin Barwell, James Wharton, Nicola Blackwood, Rob Wilson and Edward Timpson going, along with Cabinet Office minister Ben Gummer, the author of the widely criticised Tory manifesto.
But former London mayoral candidate Zac Goldsmith returned for the Tories in Richmond Park with a majority of just 45 some six months after losing it to the Liberal Democrats.
Ukip leader Paul Nuttall faced calls to quit after suffering humiliation in Boston & Skegness, where he came in a distant third, and the eurosceptic party lost its only Westminster seat in Clacton .
Ukip MEP Bill Etheridge said "heads must roll" to save the party.
High-profile casualties of a night of shock defeats included Liberal Democrat former leader and ex-deputy prime minister Nick Clegg in Sheffield Hallam, Scotland's former first minister Alex Salmond in Banff & Buchan and the SNP's leader in Westminster Angus Robertson in Moray.
Home Secretary Amber Rudd and Education Secretary Justine Greening hung onto their seats by the skin of their teeth with much reduced majorities.
Accepting victory in Islington North, Mr Corbyn said voters had opted for hope and "turned their backs on the politics of austerity".
In an attack on Mrs May he said: "The Prime Minister called the election because she wanted a mandate.
"Well the mandate she has got is lost Conservative seats, lost votes, lost support and lost confidence.
"I would have thought that's enough to go, actually, and make way for a government that will be truly representative of all the people of this country."
Speaking as she was re-elected MP for Maidenhead, Mrs May said: "At this time, more than anything else, this country needs a period of stability."
As the party with the most seats and votes "it will be incumbent on us to ensure that we have that period of stability and that is exactly what we will do".
Asked if Mrs May could remain as Tory leader, Ms Soubry told the BBC: "She's a remarkable and very talented woman and she doesn't shy away from difficult decisions, but she now has to obviously consider her position."
Mrs May drove direct from the Maidenhead count to Conservative HQ in London for crunch talks with aides as dawn broke before moving on to 10 Downing Street.
Labour deputy leader Tom Watson said: "Theresa May's authority has been undermined by this election. She is a damaged Prime Minister whose reputation may never recover."
Mr Osborne said there would be "a very big post mortem coming"
Brexit Secretary David Davis said he would "fight tooth and nail" to keep Mrs May in post, and dismissed suggestions he might be a contender to replace her.
"The simple truth is we have a Prime Minister, she is a very good leader, I'm a big supporter of hers," Mr Davis told the Press Association.
"I'll fight tooth and nail to keep her in place."
Foreign Secretary Boris Johnson, often tipped as a potential successor to Mrs May as Tory leader, said: "We've got to listen to our constituents and listen to their concerns."
Liberal Democrats were celebrating the return of former ministers Sir Vince Cable, Sir Ed Davey and Jo Swinson two years after they lost their parliamentary seats.
And Tim Farron's party took Bath back from the Conservatives and regained Caithness, Sutherland & Easter Ross and Edinburgh West, which were lost to the SNP in 2015.
Mr Farron held on to his Westmorland & Lonsdale seat in Cumbria on a much-reduced majority, down from 8,949 in 2015 to just 777 now.
Labour took Canterbury, a seat which had been held by Conservatives since 1918, and claimed Tory scalps in a string of seats including Bristol North West, Stroud, Warwick & Leamington, Stockton South and Vale of Clwyd.
The closest result of the night came as SNP Europe spokesman Stephen Gethins held off a Liberal Democrat challenge for his North East Fife seat with a winning margin of just two.
Election 2017: Your complete guide to every Yorkshire resultElection 2017: So what happens now with a hung parliament?General Election 2017: Live news & reaction in Yorkshire and across UKFind friends and understand Facebook: Advice for new MPs‘Greatest privilege’: Nick Cleggs’ 12 years in Sheffield Hallam comes to an endJames Reed: Theresa May’s reputation in tatters after election gamble failsThey said what? Through the night of the 2017 General Election in quotes