One of 15 children, Ngata was born in Te Araroa (then called Kawakawa), a small coastal town about 175 kilometres north of Gisborne, New Zealand. His iwi was Ngāti Porou, and his father was considered an expert in traditional lore. Ngata was greatly influenced both by his father and by his great - uncle Ropata Wahawaha (who had led Ngāti Porou forces in the land wars). Ngata was raised in a Māori environment, speaking the Māori language, but his father also ensured that Ngata learned about the Pākehā world, believing that this understanding would be of benefit to Ngāti Porou.

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, Maori or Pakeha, to gain a double degree).

In 1895, a year before finishing his law degree, 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. Apirana and Arihia had eight children, four girls and four boys.

Shortly after Ngata's legal qualifications were recognised, he and his wife returned to Waiomatatini where they built a house. Ngata quickly became prominent in the community, making a number of efforts to improve the social and economic conditions of Māori across the country. He also wrote extensively on the place of Māori culture in the modern age. At the same time, he gradually acquired a leadership role within Ngāti Porou, particularly in the area of land management and finance.

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.

In the First World War, Ngata was highly active in gathering Māori recruits for military service, working closely with Reform Party MP Maui Pomare. Ngata's own Ngāti Porou were particularly well represented among the volunteers. The large Māori commitment to the war, much of which can be attributed to Ngata and Pomare, created a certain amount of goodwill from Pākehā towards Māori, and assisted Ngata's later attempts to resolve land grievances.

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. 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.

During this time, 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. 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, encouraging the creation of a Māori bishopric. Throughout all this, Ngata also remained deeply involved in the affairs of his Ngāti Porou iwi, particularly as regards land development.

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

In the 1928 elections, 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, both Ngata's wife and eldest son died of illness.

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 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, although no real evidence of this was ever presented. Ngata, while denying any personal wrongdoing, accepted responsibility for the actions of his department and resigned from his ministerial position. Many Māori were angry at Ngata's departure from Cabinet, believing that he was the victim of a Pākehā attempt to undermine his land reforms.

Although Ngata had resigned from Cabinet, he still remained in Parliament. In the 1935 elections, 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 elections, when he was finally defeated by a Labour - Ratana candidate, Tiaki Omana. He stood again for his seat in the 1946 elections, but was unsuccessful.

Despite leaving Parliament, Ngata remained involved in politics. 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. In 1950, he was appointed to Parliament's upper house, the Legislative Council, but was too ill by this time to take his seat.

Ngata died in Waiomatatini on 14 July 1950. He is remembered for his great contributions to Māori culture and language. His image appears on New Zealand's $50 note.

On October 19, 2009, Apirana 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. Apirana Ngata has one surviving child, his youngest son, Sir Henare Ngata (born 1918).