New Zealand national politics have featured a pervasive party system since the early 20th century. Usually, all members of Parliament's unicameral House of Representatives belong to a political party. Independent MPs do not occur often.

While two major parties (namely Labour and National) have dominated the New Zealand national political landscape since the 1930s, the introduction of proportional representation in 1996 led to a multi-party system, such that smaller parties have substantial representation in Parliament and can now reasonably expect to gain seats in government. As of 2024^[update], six parties have MPs in the 54th Parliament.

New Zealand's party system did not arise until the late 19th century. Before this, members of Parliament stood as independent candidates, and while some MPs joined factions, these typically were formed around prominent individuals such as Julius Vogel, and did so after an election, not before.^[1]

The Liberal Party, which was formed in 1891, was New Zealand's first 'modern' political party.^[2] It was the country's sole political party until the formation of the more conservative Reform Party in 1909.^[1] The Labour Party was founded in 1916, and by 1919 these three parties dominated New Zealand politics.^[1]

The Liberal Party was succeeded by the United Party in 1928.^[3] The United and Reform parties found themselves working together more often, and they formed a coalition in 1931.^[3] After Labour won office in 1935,^[1] United and Reform formally amalgamated in 1936 to form the National Party.^[4] The first-past-the-post (FPP) plurality voting system (in use before the 1990s) entrenched a two-party system, since the two major parties usually won far more seats than their share of the overall vote.^[5]

Over the years, a number of third parties or so-called minor parties developed, notably the Social Credit Party, the New Zealand Party, the Values Party, and the Alliance.^[6] However, the FPP electoral system meant that regardless of how many votes a party gained nationwide, it could not win a seat without a plurality in a particular electorate.^[5] For example, the Social Credit Party won over 11% of the votes cast in the 1954 election but did not have a plurality in any electorate so won no seats. Similarly, in the 1984 election, the New Zealand Party received over 12% of the votes cast but also won no seats.^[7] Under such conditions, minor parties mostly performed poorly in terms of making an impact in Parliament.

In 1993, the Electoral Act 1993 was passed, introducing the mixed-member proportional (MMP) electoral system for the 1996 election. Now, voters cast both a party vote and an electorate vote. Any party that won at least 5% of the party vote entered Parliament, as could still enter through the previous electorate pathway.^[8] This made it much easier for smaller parties to enter Parliament, but more difficult to gain elected as a non-party independent.^{[citation needed]}

In the late 1990s a phenomenon originated in New Zealand's multi-party system in which MPs sitting in Parliament increasingly switched parties (or formed breakway parties), known as "waka-jumping". This is now disallowed to maintain the integrity of the party-based proportional representation.^[9]

Political parties in New Zealand can be either registered or unregistered. Registered parties must have five-hundred paying members, each eligible to vote in general elections, and party membership rules.^[10]

If a party registers, it may submit a party list, enabling it to receive party votes in New Zealand's MMP electoral system. Unregistered parties can only nominate candidates for individual electorates.^[11]

As of 2020^[update], registered political parties are also able to spend up to $1,169,000 during the campaign for the party vote and $27,500 per electorate seat. Unregistered entities are able to spend up to $330,000 on general election advertising.^[12]

• Politics of New Zealand
• Political funding in New Zealand
• List of political parties by country
• Socialism in New Zealand
• Liberalism in New Zealand