Ngata attended primary school in Waiomatatini before moving on to Te Aute College, where he received a Pākehā-style education. Ngata performed well, and his academic results were enough to win him a scholarship to Canterbury University College (now the University of Canterbury), where he studied political science and law. He gained a BA in politics in 1893, the first Māori to complete a degree at a New Zealand university, then gained an LL.B. at the University of Auckland in 1896 (the first New Zealander, Māori or Pākehā, to gain a double degree).

In 1895, a year before finishing his second degree (law), Ngata married 16-year-old Arihia Kane Tamati who was also of the Ngāti Porou iwi. Ngata had previously been engaged to Arihia’s elder sister, Te Rina, but she died. Āpirana and Arihia had fifteen children, eleven of whom survived to adulthood; six girls and five boys.

Ngata’s first involvement with national politics came through his friendship with James Carroll, who was Minister of Native Affairs in the Liberal Party government. Ngata assisted Carroll in the preparation of two pieces of legislation, both of which were intended to increase the legal rights enjoyed by Māori. In the 1905 election, Ngata himself stood as the Liberal candidate for the Eastern Maori electorate, challenging the incumbent Wi Pere. He was elected to Parliament.

Ngata quickly distinguished himself in Parliament as a skilled orator. He worked closely with his friend Carroll, and also worked closely with Robert Stout. Ngata and Stout, members of the Native Land Commission, were often critical of the government’s policies towards Māori, particularly those designed at encouraging the sale of Māori land. In 1909, Ngata assisted John Salmond in the drafting of the Native Land Act.

In late 1909, Ngata was appointed to Cabinet, holding a minor ministerial responsibility for Māori land councils. He retained this position until 1912, when the Liberal government was defeated. Ngata followed the Liberals into Opposition.

Although in Opposition, Ngata enjoyed relatively good relations with his counterparts across the House in the Reform Party. He had a particularly good relationship with Gordon Coates, who became Prime Minister in 1925 and later Princess Te Puea of Waikato. The establishment of several government bodies, such as the Māori Purposes Fund Control Board and the Board of Māori Ethnological Research, owed much to Ngata’s involvement.

Ngata was knighted in 1927, only the third Māori (after Carroll and Pomare) to receive this honour.

Ngata was also active in a huge variety of other endeavours. The most notable, perhaps, was his involvement in academic and literary circles – in this period, he published a number of works on significant Māori culture, with Nga moteatea, a collection of Māori songs, being one of his better known works. Ngata was also heavily involved in the protection and advancement of Māori culture among Māori themselves, giving particular attention to promoting the haka, poi dancing, and traditional carving that had been begun by Te Puea. One aspect of his advocacy of Māori culture was the construction of many new traditional meeting houses throughout the country. Yet another of Ngata’s interests was the promotion of Māori sport, which he fostered by encouraging intertribal competitions and tournaments. Finally, Ngata also promoted Māori issues within the Anglican Church in New Zealand, encouraging the creation of a Māori bishopric. In December 1928, Frederick Bennett, was consecrated as suffragan bishop to the Waiapu diocese with the title Bishop of Aotearoa. Ngata and Bishop Herbert Williams campaigned for the recognition of Māori language as a subject for study in the University of New Zealand, with the study of Māori becoming eligible for a degree of bachelor of arts in 1928.

In the 1928 election, the United Party (a rebranding of the old Liberal Party, to which Ngata belonged) won an unexpected victory. Ngata was returned to Cabinet, becoming Minister of Native Affairs. He was ranked third within Cabinet, and occasionally served as acting Deputy Prime Minister. Ngata remained extremely diligent in his work, and was noted for his tirelessness. Much of his ministerial work related to land reforms, and the encouragement of Māori land development. Ngata continued to believe in the need to rejuvenate Māori society, and worked strongly towards this goal.

In 1929, Ngata’s wife Arihia Ngata and his eldest son Mākarini died of dysentery. After Arihia’s death, Ngata married Te Rīringi Tūhou in 1932.

In 1932 Ngata and his Department of Native Affairs came under increasing criticism from other politicians. Many believed that Ngata was pressing ahead too fast, and the large amount of activity that Ngata ordered had caused organizational difficulties within the department. An inquiry into Ngata’s department was held, and it was discovered that one of Ngata’s subordinates had falsified accounts. Ngata himself was severely criticised for disregarding official regulations which he had often felt were inhibiting progress. It was also alleged that Ngata had shown favouritism to Ngāti Porou and Waikato, especially Te Puea and her husband Rawiri Tumokai Katipa. Bob Semple, a leading Labour politician, said the Royal Commission investigation showed one of the worst specimens of abuse of political power, maladministration, misappropriation of public funds as well as a betrayal of trust. Ngata, while denying any personal wrongdoing, accepted responsibility for the actions of his department and was dismissed from his ministerial position.

Throughout all this, Ngata also remained deeply involved in the affairs of his Ngāti Porou iwi, particularly as regards land development. He was instrumental in establishing the land incorporation scheme whereby unused Māori land with multiple owners was amalgamated under a farm manager—often Pākehā, who developed and ran the farm. In government he was able to arrange for the transfer of four blocks of farm land to Te Puea Herangi and her husband. He arranged grants and government loans to help her develop farms for Waikato. He fired the Pākehā farm manager and replaced him with Te Puea. He arranged a car for her so she could travel around her estates. In 1934, during the depression, the public, media and parliament became alarmed at the large sums of money being gifted to Te Puea and others. A royal commission was held and Ngata was found guilty of irregularities in expenditure and negligence in administration, but no major scandals were unearthed. His land projects up to 1934 had involved the expenditure of £500,000, most of which was recoverable. Ngata resigned in December 1934. Ngata fought for higher living standards for the Māori people, and was very active during an economic depression in New Zealand in the Thirties, developing large farms which provided jobs and helped to restore the dignity of many Māori.

Although Ngata had resigned from Cabinet, he still remained in Parliament. He was awarded the King George V Silver Jubilee Medal in 1935. In the 1935 election, the Labour Party was triumphant – Ngata went into Opposition, although the new Labour government retained many of his land reform programs. Ngata remained in Parliament until the 1943 election, when he was finally defeated by a Labour-Rātana candidate, Tiaki Omana. He had been a member of parliament for almost 38 consecutive years, breaking the previous record of 32 years set by James Carroll and coming close to Maurice O’Rorke overall record of nearly 39 years. Both marks were later surpassed by Rex Mason.

Ngata stood again for his seat in the 1946 election, but was unsuccessful. He remained involved in politics despite leaving Parliament. He gave advice on Māori affairs to both Peter Fraser (a Labour Prime Minister) and Ernest Corbett (a National Minister of Māori Affairs), and arranged celebrations of the Treaty of Waitangi’s centenary in 1940. In the Second World War, he once again helped gather Māori recruits. On 22 June 1950, he was appointed to Parliament’s upper house, the Legislative Council, but was too ill by this time to take his seat.

In 1948, Ngata’s second wife, Lady Te Rīringi, died, and he married Hēne Te Kira not long before his own death.

On 7 May 1948, Ngata received an honorary doctorate in literature (LittD) from the Victoria College. At the same ceremony, his youngest son Henare graduated with a Bachelor of Arts.

Ngata died in Waiomatatini on 14 July 1950, following a brief illness, and was buried beside his first wife Lady Arihia behind their home ‘The Bungalow’ in Waiomatatini. He is remembered for his great contributions to Māori culture and language. His image appears on New Zealand’s $50 banknote.

Sir Āpirana and Lady Arihia Ngata guided the design of the St. Michael and All Angels’ Chapel at Hukarere Girls College, and the chapel was consecrated on 1 November 1953.

On 19 October 2009, Āpirana Ngata’s last surviving daughter, Mate Huatahi Kaiwai (born Ngata), died at her residence at Ruatoria, East Cape, New Zealand, aged 94. She was interred next to her late husband Kaura-Ki-Te-Pakanga Kaiwai and her son Tanara Kaiwai at Pukearoha Urupa. In the 2004 New Year Honours she had been made a Companion of the Queen’s Service Order (QSO) for community service.

Ngata’s youngest son, Sir Henare Ngata, died on 11 December 2011 aged 93. He was Māori vice-president of the National Party from 1967 to 1969 and stood as the National Party candidate for Eastern Māori in 1969.