New Zealand's MMP system and why coalitions decide its elections

New Zealand's 54th parliament convenes for its final sitting this week, with the country due to vote on November 7. Opinion polls point to a tight contest, with neither the left nor the right bloc holding a decisive lead, leaving the outcome to be settled by the country's electoral rules.

A system built for inclusion

New Zealand replaced the British-style first-past-the-post model with mixed-member proportional representation, or MMP, roughly three decades ago. The switch followed a commission's recommendation, driven by concern that smaller parties were being shut out of parliament. MMP originated in Germany and has since been adopted, sometimes in modified form, by countries including Bolivia, Lesotho, South Korea and Thailand.

Since its introduction, every government has been a coalition between the centre-left Labour Party or the centre-right National Party and smaller partners, with one exception: 2020, when Labour won a outright majority after its handling of the early phase of the COVID-19 outbreak.

How voters decide

Each voter casts two ballots — one for a preferred constituency candidate and one for a party. The candidate with the most votes in a constituency becomes an MP, while the party vote determines how many seats each party holds in parliament.

Winners in the country's 71 constituencies take their seats automatically. The remaining seats are drawn from party lists so that each party's total share matches its nationwide vote. About 49 list seats are expected this election, though the figure can vary.

To enter parliament at all, a party must win at least 5% of the party vote or secure at least one electorate seat. A party or coalition needs a majority in the single-chamber parliament — usually at least 61 of 120 seats — to form a government.

Minor parties as kingmakers

Because of MMP's design, smaller parties often hold the balance of power. New Zealand First has played this role most prominently, backing National after the 1996 election and Labour after 2017. Te Pati Maori has also supported National-led governments, doing so after the 2008, 2011 and 2014 elections. This time, the centrist Opportunity Party could become pivotal if it crosses the 5% threshold or wins an electorate seat.

The 2017 election illustrated how the largest party does not always end up governing. National won 56 seats against Labour's 46 but could not assemble a majority; Labour went on to form a government through a coalition with New Zealand First and a confidence-and-supply agreement with the Green Party.

Overhang and Maori seats

Parliament normally has 120 seats, but extra seats can be added when a party wins more electorate seats than its share of the party vote would entitle it to. That occurred after the 2023 election, when Te Pati Maori won six electorates on 3.1% of the party vote. Polls suggest the situation could recur in 2026.

Seven electorate seats are Maori electorates, reserved for voters who choose to enrol on the Maori electoral roll. Maori voters may instead opt to enrol in a general electorate.