New Zealand is a constitutional monarchy and a parliamentary democracy. Queen Elizabeth II, represented in the country by a governor-general, remains head of state, but executive power is effectively held by the prime minister and cabinet.

The prime minister is appointed by the governor-general, and is generally the leader of the party or coalition holding the majority of seats in the House of Representatives. The cabinet is appointed by the governor-general on the recommendation of the prime minister.

The unicameral House of Representatives has 120 members, elected under a form of proportional representation (known as mixed member proportional, or MMP) for three years. The MMP system is designed to avoid domination by a majority group and gives a voice to minorities.

There is universal adult suffrage, and voters have both an electorate vote and a party vote. The former is used to select the local MP (since the 2001 census, 69 are elected on first-past-the-post constituencies, including seven representing Maori constituencies), while the latter is used to select a party and determine the total number of seats for each party in parliament. All parties polling more than 5% of the vote (or with at least one electorate seat) are entitled to further seats based on the proportion of party votes cast. Normally 51 members are party MPs but this number can be increased (increasing the total number of seats in parliament for the term) when a party wins more electorate seats than it is entitled to according to the party vote. This happened for the first time in September 2005.

The Supreme Court was established in 2004 as the final court of appeal, replacing the UK’s Privy Council. The High Court and District Court have jurisdiction in both civil and criminal matters, the High Court for the most serious cases. In the more serious criminal cases, whether in the High Court or District Court, defendants have the right to trial by jury. The Court of Appeal hears appeals from the High Court, and from trials by jury in the District Court, and the High Court hears appeals from the lower courts and tribunals.

The Family Court is a division of the District Court, and Justices of the Peace deal with minor criminal cases. The specialised tribunals include the Employment Tribunal, the Disputes Tribunal, the Waitangi Tribunal, the Environment Court and the Deportation Review Tribunal.