The principal roles and tasks expected of the NZDF is to provide a combat capable force to defend New Zealand's sovereign territory, and protect critical lines of communication.

[8][9] After the Treaty of Waitangi in 1840, New Zealand's security was dependent on British Imperial troops deployed from Australia and other parts of the empire.

[18] In June 1845, 75 members of the Auckland Militia under Lieutenant Figg became the first unit to support British Imperial troops in the Flagstaff War, serving as pioneers.

On 28 October 1846, with the passing of the Armed Constabulary Ordinance in 1846, a fresh call was made by Mr Donnelly of the Legislature to do away with the Militia because of its expense.

[28] The cost to Britain of maintaining a military force in New Zealand was considerable, prompting a dispatch on 24 November 1846 from The Right Hon Earl Grey to advise Lieutenant Governor George Grey that ... the formation of a well-organised Militia and of a force of Natives in the service of Her Majesty, would appear to be the measures most likely to be successfully adopted.

[29] Further pressure in the early 1850s from Britain for removing their forces prompted pleas for them to remain as the Militia were deemed insufficient for the purpose.

This war began to involve the major European powers and exposed New Zealand and Australia to a possible external threat from the Imperial Russian Navy.

[37] By late 1859 the number of volunteer units was so great that Captain H C Balneavis was appointed Deputy Adjunct-General, based at Auckland.

[52] In October 1864 the Government decided to reduce the numbers in the Colonial Defence Force to 75 with three units of 25 members each in Wellington, Hawkes Bay and Taranaki.

[54] Parliamentary debates in late 1864 also supported this view, especially as the cost of maintaining the Imperial troops was becoming a greater financial burden on the colony.

This proposed an armed constabulary force supported by friendly natives, volunteer units, and militia as the case may require be established to take the place of the Imperial troops.

They were to be divided into 30 companies of 50 men each based as follows: The total Defence budget, which included purchasing a steamer for use on the Waikato, Patea, and Wanganui rivers, was 187,000 pounds per annum.

From 1863 to 1867 Forest Ranger volunteer units were formed, tasked with searching out Maori war parties, acting as scouts, and protecting lines of communication.

A combined Australian and New Zealand Army Corps (ANZAC) was formed for the Gallipoli campaign during World War I, and its exploits are key events in the military history of both countries.

In 2023, North & South and Radio New Zealand reported that the NZDF was experiencing a high attrition rate in the two-year period between 2021 and 2023 due to poor salaries and living conditions at military accommodation.

[64][65] According to North and South contributor Peter McKenzie, 77% of NZDF personnel were paid between 5% and 16% less than people in equivalent civilian jobs.

[64] In April 2023, Radio New Zealand reported that the high attrition rate had limited the NZDF's response to Cyclone Gabrielle, its ability to crew three naval offshore patrol vessels, and accelerated the Air Force's decommissioning of its fleet of P-3K2 Orions.

[65] In July 2024, the NZDF confirmed that it would be investing NZ$490 million to expand and upgrade housing at the Waiouru Military Camp in partnership with local iwi (tribe) Ngāti Rangi over the next 25 years.

The Aitken St facility initially was home to around 900 employees of the NZDF, the New Zealand Security Intelligence Service (NZSIS) and the New Zealand Ministry of Defence; the NZSIS moved across to Pipitea House in early 2013,[68] and the NZDF were forced to vacate the Aitken St building after the 2016 Kaikōura earthquake, which seriously damaged the building.

[75] Another female officer, Colonel Helen Cooper, had previously held the post of Deputy Chief of Army though in an acting capacity without being promoted to the customary rank of Brigadier.

[77] This includes starting the Defence Force KiwiSaver scheme, and appointing financial advisers[78] to support the welfare of members.

The RNZN possess two Anzac class frigates, developed in conjunction with Australia, based on the German MEKO 200 design.

The deployment included the vessels HMNZS Canterbury, Te Kaha and Endeavour, six Iroquois helicopters, two C-130 Hercules and an infantry battalion.

New Zealand shares training facilities, personnel exchanges, and joint exercises with the Philippines, Thailand, Indonesia, Papua New Guinea, Brunei, Tonga, and South Pacific states.

After the 1986 anti-nuclear legislation that refused access of nuclear-powered or armed vessels to ports, the USA withdrew its obligations to New Zealand under ANZUS.

Due to the US policy at that time of "neither confirm nor deny", ship visits ceased although NZ and the USA remained "good friends".

The NZDF served alongside NATO-led forces in Afghanistan in the first decade of the twenty-first century, and in 2004 the NZSAS was awarded a Presidential Unit Citation by US President George W Bush for "extraordinary heroism" in action.

[86] New Zealand is a member of the ABCA Armies standardisation programme, the naval AUSCANNZUKUS forum, the Air and Space Interoperability Council (ASIC, the former ASCC, which, among other tasks, allocates NATO reporting names) and other Western 'Five Eyes' fora for sharing signals intelligence information and achieving interoperability with like-minded armed forces, such as The Technical Cooperation Program (TTCP).

[88] In June 2019, the Government established a new NZ$11 million facility at Whenuapai Airbase in Auckland to support plans to raise the cohort of LSV trainees to 1,600 in 2020.

It also reported that NZDF staff were overwhelmed by participants' behavioural problems, with at least ten personnel experiencing serious mental harm including suicide ideation.