Travelling the country, Ngata promoted the Young Māori Party whose role it was to foster legislation directly beneficial to Māori.
He entered parliament in 1905 and served until 1943, initiating the Māori Land Development Scheme. This scheme provided government funding to Māori landowners to develop the physical infrastructure of their farms and to encourage the amalgamation of land titles into single administrative structures. This led to raising health standards of iwi and providing equal opportunity in higher education.
Ngata was part of the contingent committee who formed the Māori Pioneer Battalion in World War I and was responsible for the 28th Māori Battalion in World War II. He noted: "We are of one house, and if our Pākehā brothers fall, we fall with them."
He was a driving force in attempting to revive Māori language, history and traditions. Ngata chaired the New Zealand Geographic Board, was president of the Polynesian Society, and a member of the Board of Trustees for the Dominion Museum (the original national museum of New Zealand - predating Te Papa Tongarewa).
Ngata encouraged the resurgence of carving, instigated the construction of Te Whare Rūnanga (House of Assembly) at Waitangi, as well as other wharenui, meeting houses, around the country.
In 1888, as a young teenager, Ngata started recording oral histories and waiata (songs) about events both predating the migration of Māori to Aotearoa and up to the present day. Published in 1929, the Ngā Mōteatea volumes are a significant and valuable repository of Māori knowledge.