The Fixed-term Parliaments Act 2011 (c. 14) (FTPA) was an act of the Parliament of the United Kingdom which, for the first time, set in legislation a default fixed election date for general elections in the United Kingdom. It remained in force until 2022, when it was repealed by the Dissolution and Calling of Parliament Act 2022. Since then, as before its passage, elections are required by law to be held at least once every five years, but can be called earlier if the prime minister advises the monarch to exercise the royal prerogative to do so. Prime ministers have often employed this mechanism to call an election before the end of their five-year term, sometimes fairly early in it. Critics have said this gives an unfair advantage to the incumbent prime minister, allowing them to call a general election at a time that suits them electorally. While it was in force, the FTPA removed this longstanding power of the prime minister.

Under the FTPA, general elections were automatically scheduled for the first Thursday in May of the fifth year after the previous general election, or the fourth year if the date of the previous election was before the first Thursday in May. However, the FTPA also provided two ways to call an election earlier. One was a Commons vote of no confidence in the government, which still required only a simple majority of voters. The other was a vote explicitly in favour of an earlier election, which required a qualified majority of two-thirds of the total membership of the Commons. The first election under the FTPA was held on 7 May 2015. An early election was held in 2017, after Prime Minister Theresa May received approval to call it by a two-thirds majority.

Under the FTPA, the following general election was scheduled for 2022, but the Early Parliamentary General Election Act 2019, passed with Opposition support, circumvented the FTPA, providing for an election on 12 December 2019 while otherwise leaving the FTPA in place. The Conservative Party entered the election with a manifesto pledge to repeal the FTPA. The resulting Conservative majority government, in fulfilment of its commitment, published on 1 December 2020 a draft Fixed-term Parliaments Act 2011 (Repeal) Bill to repeal the FTPA and revive the royal prerogative power of dissolving Parliament as it existed before the act. The repealing legislation was formally announced in the Queen's Speech of 11 May 2021, and granted royal assent as the Dissolution and Calling of Parliament Act 2022 on 24 March 2022.

The Parliament of England originated as a board of advisors for the monarch, or curia regis. As the king was able to summon Parliament at will, so could he dissolve it by royal proclamation. Events of the 17th century began to regulate the summoning and dissolution of Parliament; the English Civil War was in large part caused by the efforts of Charles I to rule without it. The Triennial Act 1640 (16 Cha. 1. c. 1) was passed to require Parliament meet for at least one session every three years, providing for a failsafe mechanism should the king fail to issue the appropriate writs; this was replaced by the Meeting of Parliament Act 1694 (6 & 7 Will. & Mar. c. 2), requiring annual sessions and a general election at least every three years.

The Septennial Act 1715 (1 Geo. 1. St. 2. c. 38) increased the maximum lifespan of a parliament to seven years. The Chartists demanded annual parliamentary elections, which was the only demand of theirs that was not achieved by the early 20th century. The Parliament Act 1911 ([1 & 2 Geo. 5]]. c. 13) amended the Septennial Act by reducing the lifespan to five years. These laws can be, and have been, abrogated in times of great crisis, in practice during both World Wars, whose respective parliaments lasted from 1910 to 1918 and from 1935 to 1945.

Despite these regulations, the royal prerogative to dissolve Parliament within the bounds of law remained. Events of the 18th and 19th century reduced the monarch's personal power in politics in favour of that of his nominal advisor the prime minister, such that by the 19th century prime ministers had a great deal of de facto control over the timing of general elections. The handing of such power to the prime minister was a convention rather than any formal law, and the monarch could (and, since the repeal of the FTPA, can) in theory refuse to grant such a request; the Lascelles Principles formulated in 1950 outline the possible scenarios in which such a refusal would likely be made.

The statutory lifespan referred to the lifetime of the parliament and not to the interval between general elections. For example, while John Major's government lasted four years, eleven months and two days; the period between the general elections of 1992 and 1997 was five years and twenty-two days. No parliament in practice ever reached this milestone outside of the World Wars, as it was always dissolved before its expiry. The longest Parliament preceding the FTPA, other than during wartime, was the 51st Parliament (1992–1997), which lasted four years, eleven months and two days.

The lack of a fixed parliamentary term allowed for the prime minister to decide when to hold an election solely on partisan grounds; it was also criticised for creating uncertainty before the calling of an election when such a calling was anticipated.