The New Zealand electoral system has been mixed-member proportional (MMP) since the 1996 election. MMP was introduced following a referendum in 1993. It replaced the first-past-the-post (FPP) system New Zealand had previously used for most of its history. New Zealanders elect their members of parliament (MPs) with two votes. The first vote is for a candidate from an electorate (electoral district). The second vote is used to elect ranked party lists.

New Zealand has a single-house legislature, the House of Representatives, usually with 120 members, although the number can increase because of (generally) one or two overhang seats, depending on the outcome of the electoral process. The 53rd Parliament, elected in 2020, has 120 seats: 72 were filled by electorate MPs, with the remaining 48 filled by list MPs according to each party's share of the party vote. New elections are held for the New Zealand Parliament at least every three years.

In 1893, New Zealand was the first country in the world to grant women the right to vote. This meant that, theoretically, New Zealand had universal suffrage from 1893, meaning all adults 21 years of age and older were allowed to vote (in 1969 the voting age was lowered from 21 to 20. It was lowered again to 18 in 1974). However, the voting rules that applied to the European settlers did not apply to Māori, and their situation is still unique in that a number of seats in the New Zealand Parliament are elected by Māori voters alone.

In contemporary New Zealand, generally all permanent residents and citizens aged 18 or older are eligible to vote. The main exceptions include citizens who have lived overseas continuously for too long, and convicted persons who are detained in a psychiatric hospital or serving a prison term of more than three years.