A two-party system is a political party system in which two major political parties consistently dominate the political landscape. At any point in time, one of the two parties typically holds a majority in the legislature and is usually referred to as the majority or governing party while the other is the minority or opposition party. Around the world, the term is used to refer to one of two kinds of party systems. Both result from Duverger's law, which demonstrates that "winner-take-all" or "first-past-the-post" elections produce two dominant parties over time.Wong Chin Huat, fz.com, July 29, 2013, When winner takes all , Accessed August 12, 2013, "...This "winner-takes-all" characteristic of political contestation then forces political groups to consolidate into two blocs, hence, the two-party system..."Regis Publishing, The US System: Winner Takes All, Accessed August 12, 2013, "...Winner-take-all rules trigger a cycle that leads to and strengthens a system of few (two in the US) political parties..." (in Wayback Machine)
The first type of two-party system is an arrangement in which all (or nearly all) elected officials belong to one of two major parties. In such systems, minor or third parties rarely win any seats in the legislature. Such systems exist, for example, in the United States, the Bahamas, Jamaica, and Zimbabwe.The Two Party System, Boundless Publishing, Two-party systems are prominent in various countries, such as the U.S., and contain both advantages and disadvantages , Accessed August 12, 2013 "...There are two main reasons winner-takes-all systems lead to a two-party system...",Eric Black, Minnpost, October 8, 2012, Why the same two parties dominate our two-party system , Accessed August 12, 2013, "...SMDP (single-member districts, plurality) voting system. ... This forces those who might favor a minor party candidate to either vote for whichever of the two biggest parties the voter dislikes the least, or to risk the likelihood that their vote will be "wasted" or, worse, that they will end up helping the major-party candidate whom the voter dislikes the most to win. Minor parties aren't banned, but they seldom produce a plurality winner, and their lack of success often causes the minor parties to wither and die...."History Learning Site, Why America is a two-party state , Accessed August 12, 2013, "...The American electoral system – winner-takes-all – guarantees that any third, fourth party etc has no chance of winning...." In such systems, while chances for third-party candidates winning election to major national office are remote, it is possible for factions within the larger parties to exert influence on one or even both of the two major parties.Patrick Bashan, CATO Institute, June 9, 2004, Do Electoral Systems Affect Government Size? , Accessed August 12, 2013, "...The current system has many disadvantages, most notably its propensity to discriminate against minor parties operating outside the increasingly uncompetitive, cozy two-party system.... America's winner-takes-all electoral system may be the least bad option for those seeking to limit government involvement in the nation's economic life...."George F. Will, October 12, 2006, Washington Post, From Schwarzenegger, a Veto for Voters' Good , Accessed August 12, 2013, "...That electoral vote system (combined with the winner-take-all allocation of votes in all states but Maine and Nebraska) makes it very difficult for third-party presidential candidates to be competitive..."Ashley Ford, September 17, 2012, Cavalier Daily, Party of three: A third political party is an important aspect of the Virginia democratic process , Accessed August 12, 2013, "...The two party system forces the third party to join their group in a winner take all system..."Two Party System, PBS, Two-Party System , Accessed August 12, 2013, "...Third-party or independent candidates face a slew of obstacles in American politics, from limited media coverage to legal barriers and Congressional leadership rules. Laws regarding third-party candidates also vary from state to state, presenting additional difficulties...."Chris Cillizza and Aaron Blake, May 18, 2012, The Washington Post, Americans Elect and the death of the third party movement , Accessed August 11, 2013
Two-party system also indicates an arrangement, common in parliamentary systems, in which two major parties dominate elections, but in which there are viable minor parties and/or independents regularly elected to the legislature. These successful minor parties are often regional parties. In these systems, the two major parties exert proportionately greater influence than their percentage of voters would suggest, and other parties may frequently win election to local or subnational office. Canada, the United Kingdom, Australia, and New Zealand are examples of countries that have this kind of two-party system.
Africa Ghana The Republic of Ghana since its transition to democracy in 1992 have a strongly institutionalized two-party system led by New Patriotic Party and National Democratic Congress.
Zimbabwe The politics of Zimbabwe are effectively a two-party system between the Robert Mugabe founded Zimbabwe African National Union-Patriotic Front and the opposition coalition Movement for Democratic Change.
Asia Bhutan
Bhutan has a unique, constitutionally mandated two-party system. According to Article 15 of the Constitution of Bhutan, parliamentary elections are conducted in two rounds. In the primary round, all registered political parties participate. However, only the top two political parties with the highest number of votes nationwide are permitted to advance to the general election to contest seats in the National Assembly. This electoral design effectively guarantees a two-party composition in the legislature after every election cycle. Lebanon
The Parliament of Lebanon is mainly made up of two bipartisan alliances. Although both alliances are made up of several political parties on both ends of the political spectrum the two-way political situation has mainly arisen due to strong ideological differences in the electorate. Once again this can mainly be attributed to the winner takes all thesis.
Philippines From 1946 to 1972, the Philippines was under a two-party system with the Liberal Party and the Nacionalista Party, with these two parties supplying all presidents and vice presidents, most members of Congress, and local officials.
With the declaration of martial law in 1972, the Kilusang Bagong Lipunan emerged as the dominant party, until its overthrow after the People Power Revolution in 1986. With the approval of the 1987 constitution, the Philippines is now on a multi-party system.
South Korea
South Korea has a multi-party systemThe New York Times, August 21, 2006, Post-Koizumi, dream of a two-party system , Accessed Oct. 18, 2013, quote: "...This is positive. A two-party system isn't here yet, but it's a kind of dream we have..." that has sometimes been described as having characteristics of a two-party system. Parties will have reconstructions based upon its leader, but the country continues to maintain two major parties. Currently these parties are the liberal Democratic Party of Korea and the conservative People Power Party.
Australia
House of Representatives Since the 1920s, the Australian House of Representatives (and thus the federal government) has in effect been a two-party system.
Since the end of World War II, Australia's House of Representatives has been dominated by two factions:
the centre-left Australian Labor Party the centre-right Coalition
The Coalition has been in government about two-thirds of time, broken by four periods of Labor governments: 1972–1975, 1983–1996, 2007–2013, and since 2022.
The ALP is Australia's largest and oldest continuing political party, formed in 1891 from the Australian labour movement. The party has branches in every state and territory.
The Coalition refers to the alliance between the Liberal Party of Australia (Australia's 2nd largest party) and National Party of Australia (4th largest). It was formed after the 1922 Australian federal election, when the Nationalist Party (ancestor of today's Liberal Party) lost its absolute majority, and was only able to remain in government by allying with the Country Party (now called the National Party). Under the Coalition agreement, if the Coalition forms government then the Prime Minister will be the leader of the Liberals, and the Deputy Prime Minister will be the leader of the Nationals. In theory, disagreements between the Coalition's constituent parties would lead to the Coalition splitting apart. This has happened only a few times in Australia's modern political history, and has always resulted in the Coalition coming back together by the next election. The most recent splits occurred in 2025, following Labor's landslide victory at that year's election, and in 2026, after three National Party members broke party solidarity in opposing the government's hate speech reforms, following the 2025 shooting at Bondi Beach.https://www.theguardian.com/australia-news/2025/may/20/nationals-leaving-split-coalition-liberal-party-australian-election>
One reason for Australia's two-party system is because the House of Representatives (which chooses the Prime Minister of Australia) is elected through the instant-runoff voting electoral system. Although voters can preference third parties and independents above the major parties, and the voting method has a reduced spoiler effect, there is still only one member per electoral division (ie: a winner-take-all system) and so major parties tend to win the vast majority of seats even if they need to rely on preferences to do so. For example, a Labor candidate may win a seat with 30% of the vote for Labor and 21% from Australian Greens voters who ranked Labor second.
Senate On the other hand, the Australian Senate is effectively a multi-party system, and a Senate majority matching the House is very rare. It uses single transferable vote with multiple Senators for each state/territory. This results in rough proportional representation and as a result, third parties have much more influence and often hold the balance of power. Since 2004, the Australian Greens have been the third largest party in the country, with 8-13% of the national vote and an equivalent amount of Senators. Prior to this, the Australian Democrats was the third largest party. Other current and past parties include One Nation, the Liberal Democrats and Family First.
Some Australian states have seen the rise of minor parties at either the state or federal level (eg: Centre Alliance in South Australia, Katter's Australian Party in northern Queensland, and the Shooters, Fishers and Farmers Party in western New South Wales), while some have seen long periods of dominance by one party. Some parties are absent entirely in parts of the country.
The Australian Capital Territory has had a Labor/Greens coalition government since 2012, opposed by the Liberals (Nationals not present). Labor was in government alone from 2001-2012. Notably, the ACT is the only state/territory where the Greens have been in power. In the Northern Territory, the two main parties are Labor and the Country Liberal Party (CLP), which aligns with the Coalition at the federal level. In Western Australia, the Liberal and National parties are not in a permanent coalition at the state level. At the 2021 Western Australian state election Labor won 53 out of 59 lower house seats in a landslide victory. The National Party won 4 seats making them the official opposition. The Liberals won only 2 seats, putting them on the crossbench. In New South Wales and Victoria, the main parties reflect the situation nationally: Labor versus the Coalition of the Liberals and Nationals. NSW is the only state where the Coalition has never split, but has also never merged into one party.