Portsmouth was a borough constituency based upon the borough of Portsmouth in Hampshire. It returned two members of parliament (MPs) to the Parliaments of England, Great Britain and from 1801 the House of Commons of the Parliament of the United Kingdom, elected by the bloc vote system.

The 1918 United Kingdom general election was called immediately after the Armistice with Germany which ended the First World War, and was held on Saturday, 14 December 1918. The governing coalition, under Prime Minister David Lloyd George, sent letters of endorsement to candidates who supported the coalition government. These were nicknamed "Coalition Coupons", and led to the election being known as the "coupon election". The result was a massive landslide in favour of the coalition, comprising primarily the Conservatives and Coalition Liberals, with massive losses for Liberals who were not endorsed. Nearly all the Liberal MPs without coupons were defeated, including party leader H. H. Asquith.