The 2017 United Kingdom general election took place on Thursday 8 June 2017, having been called just under two months earlier by Prime Minister Theresa May on 18 April 2017 after it was discussed in cabinet. Each of the 650 constituencies elected one Member of Parliament (MP) to the House of Commons. The governing Conservative Party remained the largest single party in the House of Commons but lost its majority, resulting in the formation of a minority government with a confidence-and-supply arrangement with the Democratic Unionist Party (DUP) of Northern Ireland.
The Conservative Party (which had governed as a senior coalition partner from 2010 and as a single-party majority government from 2015) was defending a working majority of 17 seats against the Labour Party, the official opposition led by Jeremy Corbyn. Under the Fixed-term Parliaments Act 2011 a general election had not been due until May 2020, but a call by Prime Minister Theresa May for a snap election was ratified by the necessary two-thirds vote in a 522–13 vote in the House of Commons on 19 April 2017. May said that she hoped to secure a larger majority in order to "strengthen [her] hand" in the forthcoming Brexit negotiations.
Opinion polls had consistently shown strong leads for the Conservatives over Labour. From a 21-point lead, the Conservatives' lead began to diminish in the final weeks of the campaign. In a surprising result, the Conservative Party made a net loss of 13 seats with 42.4% of the vote (its highest share of the vote since 1983), whilst Labour made a net gain of 30 seats with 40.0% (its highest share since 2001 and the first time the party had gained seats since 1997). This was the closest result between the two major parties since February 1974, and their highest combined vote share since 1970. The Scottish National Party (SNP) and the Liberal Democrats, the third- and fourth-largest parties, both lost vote share; media coverage characterised the election as a return to two-party politics. The SNP, which won 56 of the 59 Scottish seats at the previous general election in 2015, lost 21 seats. The Liberal Democrats made a net gain of four seats. UKIP, the third-largest party in 2015 by number of votes, saw its share of the vote reduced from 12.6% to 1.8% and lost its only seat. Plaid Cymru gained one seat, giving it a total of four seats. The Green Party retained its sole seat, but saw its share of the vote reduced. In Northern Ireland, the Democratic Unionist Party (DUP) won 10 seats, Sinn Féin won seven, and Independent Unionist Sylvia Hermon retained her seat. The Social Democratic and Labour Party (SDLP) and Ulster Unionist Party (UUP) lost all their seats. The Conservatives were narrowly victorious and remained in power as a minority government, having secured a confidence and supply deal with the DUP.
Negotiation positions following the UK's invocation of Article 50 of the Treaty on European Union in March 2017 to leave the EU were expected to feature significantly in the campaign, but did not. The campaign was interrupted by two major terrorist attacks in Manchester and London, with national security becoming a prominent issue in the final weeks of campaigning.