New Zealand is a constitutional monarchy with parliamentary democracy as a system of government.  It is an independent member of the Commonwealth. There are three branches of government: Executive, Legislative and Judicial. Fulfilling executive functions are head of state, prime minister and a cabinet. The legislative branch is made up of a one-chamber House of Representatives or parliament. The judicial branch consists of the Supreme Court, Court of Appeal, High Courts and District Courts. Local government has powers conferred by parliament.  It is made up of 12 regional councils with 74 territorial authorities consisting of 15 city councils, 58 rural district councils and one county council (Chatham Islands). These councils each have a directly elected mayor and council members. Territorial authorities can choose to delegate minor powers to smaller community boards.

Queen Elizabeth II is head of state, represented in New Zealand by a governor-general who has prerogative powers. The Prime Minister is head of government and leads the cabinet, which is the most senior policy-making body in the government. The Queen and governor-general cannot exercise power without the advice of the Cabinet except under certain circumstances. The current governor-general is Sir Jerry Mateparae (since 2011), and the Prime Minister is John Key (since 2008), leader of the National party coalition. Eight political parties of varying sizes make up a coalition government when the main party alone does not have enough seats in Parliament to form a majority.

The governor-general is appointed on advice of New Zealand’s Prime Minister. An executive council, all who must be members of Parliament is appointed by the governor-general on recommendation of the Prime Minister. The Prime Minister is appointed by the governor-general based on party strength and is the leader of the political party or coalition of parties that have majority in Parliament. The Prime Minister appoints members of Parliament to the cabinet. Parliament is summoned, adjourned or dissolved by the governor-general. Parliament now consists of 122 members, with seven sets reserved for Māori, who are elected on a separate roll. Māori may, however, run for non-reserved seats.

Judges in the justice system are appointed by the governor-general. The Chief Justice at present is Dame Sian Elias. The courts interpret common law in uniformity with the common law of the United Kingdom. There are specialised courts, namely employment, family, youth and the Māori Land Court.

At local government level, New Zealand has regional councils that are responsible for environmental management, regional civil defence and transportation planning; they have the power to set their own regional tax rates. Territorial authorities administer roads, sewerage and building consents among other matters. This structure was implemented in 1989. There are 12 regions and territorial authorities include 57 districts and 16 city councils.  Members of these councils are directly elected. A few smaller community boards and special-purpose bodies have members are either elected or appointed.

New Zealand has several external dependent areas: the Cook Islands and Niue, which are self-governing but in free association, and Tokelau. It also asserts a territorial claim over the Ross Dependency in Antarctica.

Voting in New Zealand is not compulsory, although enrolment to vote is. Every adult over the age of 18 is entitled to vote. Parliamentary elections are held every three years, although elections can be called earlier. In 1993, the country changed its electoral system from first past the post (FPP) to mixed member proportional (MMP), based on a German model. This is a proportional system in which each voter has an electorate vote, which goes toward the local MP, and a party list vote, which selects a party and determines the total number of seats for each party in parliament. Since this change, New Zealand government has been formed by a coalition of parties. This system is intended to increase the likelihood of minorities to gain a voice in government and to encourage policy-based voting rather than by party.