The Conservatives emerged as the biggest party but they have fallen short of an overall majority, following a strong showing by Jeremy Corbyn’s Labour Party.
May’s campaign focused on ensuring stability and delivering a strong position when negotiating Brexit with the European Union.
The UK voted in a referendum to leave the EU last year and the UK has triggered Article 50 to start the formal process of leaving, with the formal exit planned in 2019.
However, the election result has severely weakened May’s position, with calls for her resignation, especially as an election had not been due until 2020.
Negotiations are ongoing to try to form a minority government in partnership with another party.
The election has shown the power of social media, as Labour’s rise was driven by very high turnouts of younger voters, calling for “June to be the end of May”, which led to several high-profile Conservative MPs losing their seats to Labour.
While the majority of national newspapers attacked Corbyn, local campaigns on social media platforms such as Facebook and Twitter saw Labour Party activists target voters directly and urge them to vote to prevent a Conservative victory.
That campaign has seemingly paid off, but it has also left the UK in the midst of a power struggle at a critical time for the negotiations over the country's exit from the EU.
With formal discussions due to start within weeks, a leadership battle or change of government could mean there is an empty space at the negotiating table when talks are due to start.
A more EU-friendly Brexit discussion is also likely if Labour forms a coalition.
The chairman of the European People's Party, the largest grouping in the EU parliament, was reported as saying: 'One year after the decision by the British people to leave the European Union, we see that Europe, Paris for example, Berlin and even Brussels is very stable, so we are ready, and we see disorientation in London, which is not a positive thing.'
In a signal of changing attitudes to Brexit, the UK Independence Party saw its vote collapse.