[11] The Cabinet Manual describes the main laws, rules and conventions affecting the conduct and operation of the Government.

The position of prime minister belongs to the person who commands the confidence of the majority of members in the House of Representatives.

[21] The first New Zealand Constitution Act was passed in 1846, though Governor George Grey was opposed to its implementation, specifically the proposed division of the country into European and Māori districts, and stated that settlers were not ready for self-government.

[25] The Sewell Ministry constituted the first responsible government, with control over all domestic matters other than native policy.

From 7 May onward, Henry Sewell was titled "colonial secretary", and is generally regarded as having been the country's first prime minister.

[12] The legal authority of the state that is vested in the monarch, known as "the Crown", which is the source of the executive power exercised by the Government.

[41][42] The royal prerogative also includes summoning and dissolving the Parliament in order to call an election,[43] and extends to foreign affairs: the negotiation and ratification of treaties, alliances, international agreements, the right to declare war and peace, and the deployment and armament of defence forces.

[47] As per the conventional stipulations of constitutional monarchy, the king and his representative rarely intervene directly in political affairs.

[12] For example, the governor-general's power to withhold the Royal Assent to bills of parliament has been rendered ineffective by the convention.

[43] Under the conventions of the Westminster system, the Government is accountable to the House of Representatives, the democratically elected component of Parliament, rather than to the sovereign.

[48] The Government is required by convention and for practical reasons to maintain the support, or confidence, of the House of Representatives.

It also requires the support of the House for the maintenance of supply (by voting through the government's budgets) and in order to pass primary legislation.

[52] The Constitution Act 1986 stipulates that general elections must be held at least every three years,[53] making this the maximum period of time that a government can serve without seeking renewal of its mandate.

[56] The Executive Council, established under the Letters Patent 1983, is a formal body that meets to give legal effect to decisions made by the Cabinet, and to carry out various other functions, such as the making of certain appointments to government agencies and boards.

[63][64] Its decisions do not in and of themselves have legal force; however, it serves as the practical expression of the Executive Council, which is New Zealand's highest formal governmental body.

[29] The governor-general will appoint as prime minister the person most likely to receive the confidence of the House of Representatives to lead the Government.

[67] However, since the introduction of the mixed-member proportional (MMP) electoral system in 1993,[68] processes were developed to allow different parties within a coalition cabinet to "agree to disagree" on some issues.

At the start of each new parliamentary term, the governor-general gives an address prepared by the Cabinet that outlines the Government's policy and legislative proposals.

In turn, a minister bears the ultimate responsibility for the actions of their department, being answerable to the House of Representatives.

[77] There are two main tiers of elected local authorities—regional councils and territorial authorities—in some places merged into unitary authorities.