Gavin Barwell, the Conservative Housing Minister, has lost his Croydon Central seat to Labour.
Mr Barwell, the author of a book titled 'How to Win a Marginal Seat', saw a majority of just 165 in his marginal seat overturned by Labour candidate Sarah Jones.
Ms Jones received 29,873 votes to Mr Barwell's 24,221 - giving her a majority of 6,652.
Mr Barwell has served as Housing Minister in the Department for Communities and Local Government since Ms May became Prime Minister last summer.
He was responsible for one of the Tory's campaign U-turns after admitting that a pledge to build thousands of new social homes actually related to a much less affordable type of housing.
The Croydon Central MP became the third minister to lose their seat after Ben Gummer, the Cabinet Office Minister, and Jane Ellison, who serves in the Department for Health, saw their constituencies switch to Labour.
Polls predict the Conservatives are on course to win 318 seats to Labour's 267, leaving both parties short of an overall majority. As leader of the party with the most seats, Ms May will be given the first opportunity to try to form a government. She may just manage to achieve this by joining forces with the Northern Irish DUP.
If she is unable to, however, then Jeremy Corbyn could be given the chance to cobble together a "rainbow coalition" that may include the Liberal Democrats, SNP and Green Party.
The result marks a disastrous night for Theresa May, who started the campaign with a commanding poll lead but saw her advantage narrow following a lacklustre campaign.
Ms May's position as Conservative leader is now at risk, with some sources suggesting Boris Johnson, the Foreign Secretary, is already holding conversations about a possible leadership bid.
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