The 2015 United Kingdom general election was held on Thursday 7 May 2015 to elect 650 Members of Parliament to the House of Commons. It was the only general election held under the rules of the Fixed-term Parliaments Act 2011 and was the last general election to be held before the United Kingdom would vote to end its membership of the European Union (EU). Local elections took place in most areas of England on the same day.

The Liberal Democrats are a liberal political party in the United Kingdom, founded in 1988. They have been the third-largest UK political party by the number of votes cast since the 1992 general election, with the exception of the 2015 general election. They have 15 members of Parliament in the House of Commons, 84 members of the House of Lords, four Members of the Scottish Parliament and one member in the Welsh Senedd. The party has over 3000 local council seats, the third largest of the British political parties. The party holds a twice-per-year Liberal Democrat Conference, at which party policy is formulated. In contrast to its main opponents' conference rules, the Lib Dems grant all members attending its Conference the right to speak in debates and vote on party policy, under a one member, one vote system. The party also allows its members to vote online for its policies and in the election of a new leader. The party served as the junior party in a coalition government with the Conservative Party between 2010 and 2015; with Scottish Labour in the Scottish Executive from 1999 to 2007; and with Welsh Labour in the Welsh Government from 2000 to 2003 and from 2016 to 2021.