Rather than gaining seats, May's party lost about a dozen and is now trying to form a coalition government with the Democratic Unionist Party.
The Conservative Party, which has governed since 2015, had hoped to get a larger majority for the Conservatives to strengthen the position of the United Kingdom in the "Brexit negotiations" but the results have dismayed them.
May has struggled to reassert her authority after losing her parliamentary majority in Thursday's snap election, which she had been under no pressure to call.
A two-term Mayor of London, former journalist and now foreign secretary, Johnson was favourite to replace David Cameron after the Brexit vote before ally Michael Gove chose to run instead, scuppering his leadership bid. But Johnson said he backed May.
Fiona Hill also resigned as joint chief of staff.
May, however, finds herself forced into the most awkward arrangement with a party not just at odds with her on progressive issues but also potentially on Brexit and public spending too.
The change was unlikely to significantly quell unrest within the party.
Just a year ago, despite a number of its most prominent politicians being climate change deniers, the party mismanaged a renewable energy subsidy program at a cost to the British taxpayer of £490,000,000. That result was a shock, but by midday on Friday Teresa May announced a deal had been done to secure the support of the 10 DUP MPs. They formed part of May's small inner circle and were blamed by many Conservatives for the party's lackluster campaign and unpopular election platform, which alienated older voters with its plan to take away a winter fuel allowance and make them pay more for long-term care.
"As and when details are finalised both parties will put them forward", it said, referring to May's Conservative Party and the DUP.
The DUP holds an anti-abortion stance and terminations are illegal in Northern Ireland unless a woman's life is in danger or there is a serious risk to her physical or mental health.
Davidson, who is gay and set to marry an Irish catholic later this year, subsequently said she had received "categoric assurances" from Downing Street that any deal would not affect LGBTI rights. They could have asked for a second general election.
EU Budget Commissioner Guenther Oettinger said it may now be possible to discuss closer ties between Britain and the EU than May had initially planned, given her election flop.
The pound on Friday fell 1.7% against the USA dollar and 1.4 % against the euro.
The political turmoil comes a week before Britain is due to start negotiating the terms of its exit from the European Union in talks of unprecedented complexity that are supposed to wrap up by the end of March 2019, when Britain actually leaves.
Britain's typically pro-Conservative press savaged May on Saturday and questioned whether she could remain in power, only two months after she started the clock ticking on the two-year European Union divorce process.
Speaking outside Downing Street on Friday, Ms May said she could rely on her party's "friends and allies" from the party founded by Ian Paisley Snr.
"We don't know when Brexit talks start".
Former minister Anna Soubry said Mrs May should "consider her position" after a "dreadful campaign" while backbencher Heidi Allen suggested she could be out within a matter of months, depending on the Brexit negotiations.
Britain's largely pro-Conservative press questioned whether May could remain in power.
Britain's best-selling Sun newspaper said senior members of her party had vowed to get rid of May, but would wait at least six months because they were anxious that a leadership contest now could propel Labour leader Jeremy Corbyn into power.
The news comes after Ms Merkel said the negotiations should go ahead as scheduled, despite the uncertainty caused by the UK's General Election resulting in a hung Parliament.