A by-election (also spelled bye-election in Ireland), known as a special election in the United States and the Philippines, or a bypoll in India, is an election used to fill an office that has become vacant between general elections.
A vacancy may arise as a result of an incumbent's death or resignation, when the incumbent becomes ineligible to continue in office (because of a recall, a prohibited dual mandate, criminal conviction, or failure to maintain a minimum attendance), or when an election is invalidated by voting irregularities. In some cases, a vacancy may be filled by a method other than a by-election (such as the outgoing member's party nominating a replacement), or the office may be left vacant. These elections may be held at any time in the country.
An election to fill a vacancy created when a general election cannot take place in a particular constituency (such as if a candidate dies shortly before election day) may be called a by-election in some jurisdictions, or may have a distinct name (e.g., supplementary election, as in Australia).
By-elections differ from snap elections in that snap elections typically elect the entire legislative or parliamentary body, whereas by-elections are typically limited to vacant positions. However, in elections to an executive post, such as a president, a governor, or a mayor, every by-election is a snap election by definition, as there is only one elective position in the "executive body". Furthermore, recall elections are typically called before a member is removed from office, whereas by-elections are usually called after.
Origins
The procedure for filling a vacant seat in the House of Commons of England was developed during the Reformation Parliament of the 16th century by Thomas Cromwell; previously a seat had remained empty upon the death of a member. Cromwell devised a new election that would be called by the king at a time of the king's choosing. This made it a simple matter to ensure the seat rewarded an ally of the crown.Jennifer Loach. Parliament Under the Tudors. Clarendon Press. Oxford. 1990. p. 36
During the eighteen-year Cavalier Parliament of Charles II, which lasted from 1661 to 1679, by-elections were the primary means by which new members entered the House of Commons.By-Elections in British Politics. UCL Press, London. 1997 pg. 1
In assemblies
In single-member constituencies
By-elections are held in most nations that elect their parliaments through single-member constituencies, whether with or without a runoff round. This includes most Commonwealth countries, such as the United Kingdom, Canada, Australia and New Zealand, as well as non-Commonwealth countries such as France and Italy (until 2006). However, in some cases, such as the French National Assembly, by-elections are only used to fill some vacancies, with the others being filled by the assumption of a seat by a running mate nominated by the vacator. If a vacancy arises shortly before a planned general election, there is usually no by-election and the seat remains vacant until the general election.
In the United States, these contests have been called "special elections" because they do not always occur on Election Day like regular congressional elections. Special elections are held when a seat in the House of Representatives, state legislature, or local legislature becomes vacant. At the federal level, the U.S. Constitution requires that vacancies in the House of Representatives be filled with a special election (unlike the Senate, where it is up to law of the state involved to determine how the vacancy is filled). In most cases where a vacancy is filled through a special election, a primary will also be held to determine which candidates will represent the major parties.
In multi-member constituencies When one seat in a multi-member constituency becomes vacant, the consequences vary. For example, a by-election may be held to fill just the vacancy, all the seats in the constituency could be contested in the by-election, or the vacancy could be filled by other means.
Typically, party-list proportional representation systems do not hold by-elections. Instead, the most successful unelected candidate named on the vacator's list fills the vacancy automatically. However, Turkey is an exception, as it holds by-elections when too many seats become vacant in the parliament (as in 1986) or a repeat vote has to be held (as in 2003).
In multi-member district systems that do not employ party lists – single transferable vote, single non-transferable vote and plurality at-large – vacancies may be filled by a by-election. This is done, for example, in the Dáil of the Republic of Ireland (STV), in the Parliament of Vanuatu (SNTV), and in the Senate of the Philippines (Pl. AL). In those systems, alternatives to holding a by-election include:
re-determining the election results with the vacators disregarded, as in Tasmania or the Australian Capital Territory, keeping the seat vacant until the next general election. This usually occurs if a vacancy arises shortly before a planned general election (within six months in New Zealand). nominating another candidate with the same affiliation as the former member, such as European Parliament seats in the Republic of Ireland.
For the Australian Senate (in which each state forms a multi-member constituency elected via single transferable vote), the state parliament appoints a replacement in the event of a vacancy; in 1977 a referendum amended the Constitution to require that the person appointed must belong to the same political party (if any) as the Senator originally elected to that seat. The states with an upper house elected via STV (NSW, Victoria, and South Australia) use the same method, except for Western Australia, which holds a recount of ballots to determine the new winner, with sitting members retaining their seats.
In mixed systems Mixed-member proportional representation, additional member, and parallel voting systems, in which some members are chosen by party lists and some from single-member constituencies, usually hold by-elections to fill a vacancy in a constituency seat; for example, the assassination of Shinzo Abe resulted in a by-election in Yamaguchi's 4th district, which Abe represented in the House of Representatives of Japan (elected under parallel voting). If a vacancy arises in a party list seat, it would be filled in the manner usual for party-list proportional systems; for example, on the resignation of Darren Hughes from the Parliament of New Zealand in March 2011, Louisa Wall filled the seat after all the five candidates above her on the New Zealand Labour Party's list declined it.
Exceptions to this rule exist: In the German Bundestag, which uses mixed-member proportional representation, by-elections were originally held upon the vacancy of any constituency seat. This was changed in January 1953, since which time vacancies in constituency seats have been filled by the next candidate on the state list of the party which won the seat, in the same manner as vacancies among list seats. Confusingly, this change occurred alongside a switch from mixed single vote, where a single set of votes was used for both constituency and list seats, to a conventional two-vote mixed member proportional system – a change which granted constituency members an electoral mandate distinct from the party's list seats. By-elections were then only held if a vacancy arose in a constituency seat and there was no associated party list with which to fill it – typically, if the former member was elected as an independent. This was referred to as a substitute election (Ersatzwahl). Since no independents had been elected to the Bundestag since the first legislative period, no such substitute election ever took place. In the 2023 electoral reform (which most prominently changed the rules for electing constituency candidates, so that the party's lowest-performing constituency candidates would not be elected if their election would give the party seats beyond its proportional share of the vote, albeit still retaining separate sets of votes for the constituency and list seats), this has been changed again so that party candidates have to have a party list (and therefore, their vacancies would be filled from the list) and any vacancies left by independent candidates remain vacant until the next election.
In executive positions By-elections are also possible on directly-elected executive positions such as presidents, governors and mayors; in this case, such a by-election is also a snap election, as the chief executive position comprises the entire "executive body" rather than one seat among many of it. Many presidents, mostly in presidential systems but sometimes in semi-presidential and parliamentary systems as well, have vice presidents that do not necessiate such procedures.
Gubernatorial and mayoral special elections have been held in the United States.
In the Phlippines, special elections for the president and vice president are to be held if both positions are vacant at the same time, and the next scheduled presidential election is more than 18 months away.
In South Korea, presidential elections held outside schedule after the president was vacated, such as in 2025, but the winner serves an entire full term instead of just the remaining months of the original term. By-elections to local officials are also held.
By-elections for mayor and magistrates are held in Taiwan.
The mayor of Vaduz, the capital of Liechtenstein, was determined in a 2024 by-election.
Significance and consequences
Direct effects
By-elections can be crucial when the ruling party has only a small majority. In parliamentary systems, party discipline is often so strong that the governing party or coalition can only lose a vote of no confidence after losing enough supporters, whether by floor-crossing or through losing by-elections, for it to become a minority government. Examples are the Labour government of James Callaghan 1976–1979 and Conservative government of John Major 1992–1997. In the United States Senate, Scott Brown's election in 2010 ended the filibuster-proof supermajority formerly enjoyed by Democrats.
By-elections can also be important if a minority party needs to gain one or more seats to gain official party status or the balance of power in a minority or coalition situation. For example, Andrea Horwath's win in an Ontario provincial by-election in 2004 allowed the Ontario New Democratic Party to regain official party status with important results in terms of parliamentary privileges and funding.
In Australia, a by-election in 1996 in the Queensland state electoral district of Mundingburra overturned the results of the 1995 state election. In that election, held in July 1995, Wayne Goss and his Labor Party had won by a slim 45-seat majority in a 89-seat parliament. The seat of Mundingburra had been awarded to the Labor Party on the basis of a majority of 16 votes. However, in December 1995 the Court of Disputed Returns threw out the result in Mundingburra after it was found that 22 overseas military personnel had been denied the chance to vote. Consequently, a by-election for Mundingburra was held in February 1996, in which the electorate was won by the opposition Liberal Party, pushing the Goss government into minority. A vote of no confidence in the government was then passed by the opposition, with the support of Independent Liz Cunningham. Following the no confidence vote, Rob Borbidge the leader of the Nationals the senior partner in the coalition became premier until his government's defeat in the 1998 state election.
Predictive value