Hēnare Te Raumoa Huatahi Balneavis was born at Muriwai, Poverty Bay, according to family information on 26 March 1880, the only son of John Henry Balneavis, a surveyor, and his wife, Rina Matewai Wilson. His special status as an only child was signified by the name Te Huatahi, and marked him as a man of destiny. He belonged to Ngāi Tāmanuhiri through his mother and Te Whakatōhea through his father; he also had links to Ngāti Kahungunu and Ngāti Porou. His paternal grandfather, Henry Colin Balneavis, had arrived in New Zealand in 1845 with the 58th (Rutlandshire) Regiment of Foot. After fighting in the northern war he became a lieutenant colonel in the colonial forces, and in 1859 married Meri Makarina Hineahua (Hineiahua) of Te Whakatōhea.
In 1895 Te Raumoa Balneavis entered Te Aute College. With a fellow pupil, Peter Buck, he attended the first conference of the Te Aute College Students' Association in February 1897. Impressed by the ability of Apirana Ngata, who presented four papers setting out his proposals for reforming Māori society, Balneavis decided to dedicate his life to the pursuit of that vision.
After leaving school, Balneavis became a law clerk in the Gisborne office of William Rees. In 1903 he passed his examination as a native interpreter first grade. In 1906 he was appointed a clerk and interpreter in the Native Land Court at Gisborne, but his talents soon marked him out for higher office. In 1909 he was drawn to the rising political star of Apirana Ngata, who employed Balneavis as his private secretary. Ngata's role as an adviser to the native minister led to Balneavis's appointment as private secretary to the minister in 1912. He was to hold this post for 28 years, serving under a series of native ministers including W. H. Herries, Gordon Coates, Ngata, George Forbes and Michael Joseph Savage.
Balneavis's long service as private secretary was testimony to his personal qualities. Always well groomed, he had a finely balanced sense of judgement, was orderly in the preparation of documents, and had a good grasp of the facts when briefing his minister. For Pākehā ministers who held the portfolio, his bilingual and bicultural skills were invaluable. He usually accompanied the minister on tours of Māori districts, acting as interpreter and introducing the minister to the people.
This role made Balneavis a national figure in his own right. He won the confidence of his superiors and his influence helped to ensure that native ministers heard Māori concerns. His skills as a mediator led to his appointment in 1921 to report on the proposed Urewera Lands Consolidation Scheme. On this occasion, his mentor Ngata acted on the other side in the interests of Urewera Māori who did not wish to sell land. In 1926 Balneavis helped to draw up guidelines for the Tūwharetoa Trust Board, which was set up to administer Crown settlement payments. During the 1934 investigation into the Native Department, which led to Ngata's resignation as native minister, Balneavis received some criticism but emerged with his reputation largely intact.
Balneavis's interest in his Māori heritage was evident in his extensive collection of whakataukī (proverbs), which were meticulously recorded on handwritten cards. Some of these were published in the journal Te Wānanga. He kept whakapapa recording both his Pākehā and Māori ancestors, and collected Māori books related to his work. He also recorded waiata and contributed to Ngata's collection, Ngā mōteatea. Balneavis's interest in ethnography led to his involvement with the Polynesian Society, of which he was an executive member from 1925 to 1940.
Throughout his long career Balneavis was Ngata's confidant and a devoted supporter of his programme for the revitalisation of Māori society. In 1923 Ngata established the Board of Māori Ethnological Research to publish Elsdon Best's manuscripts on Māori culture and other writings by contributors to the Journal of the Polynesian Society. Balneavis became its first secretary. He was also involved with another of Ngata's projects, the Board of Māori Arts (later the Māori Arts and Crafts Board).
When the Māori Purposes Fund Control Board was established in 1924–25 Balneavis was appointed secretary. The board's funds were used to support and promote education, the Polynesian Society, ethnological research, traditional arts and crafts, the refurbishment of meeting houses and church buildings, and to help organise major hui. Ngata masterminded the board's strategy while Balneavis attended to administrative detail and execution. In 1935 the Board of Māori Ethnological Research and the Māori Arts and Crafts Board were absorbed into a new Māori Purposes Fund Board.
Balneavis was particularly invaluable to Ngata in the organisation of large tribal projects, such as the building of the meeting house Te Ikaroa-a-Māui at Waitara, a Māori Purposes Fund Board project. When the carvings were commissioned late in 1935, only nine months remained to the planned opening on 27 June 1936. That the deadline was met was testimony to Balneavis's drive and commitment. Because of his experience in organising large inter-tribal hui, he was engaged by Hapi Love to arrange the opening ceremony.
Other large hui organised by Balneavis included the reception for the prince of Wales at Rotorua in 1920, the duke and duchess of York's visit to Rotorua in 1927, the opening of the house Māhinārangi at Ngāruawāhia in 1929, the Waitangi celebrations of 1934, the duke of Gloucester's reception at Rotorua in 1934, and the opening of the Raukawa carved house at Ōtaki in 1936. Balneavis accompanied the duke and duchess of York on their 1927 tour of New Zealand as a guide and interpreter; for these and other services he was made an MVO.
Known as 'Bal' to English-speakers, and 'Rau' or Te Raumoa to Māori, Balneavis was keenly interested in sport, particularly golf and rugby: he served on the council of the New Zealand Golf Association and on the New Zealand Rugby Football Union's Māori Advisory Board.
On 8 October 1927, at Wellington, he had married Irma Leah Wallace. They had no children, and Irma was to inherit his interests in Māori land after his death. Even as his life was drawing to a close he was heavily involved, with Ngata, in organising Māori participation in the 1940 centennial celebrations. On 13 May 1940 Te Raumoa Balneavis collapsed and died at his office door in Parliament Buildings. He was buried at Whāhorehore-te-kai Māori cemetery, near Muriwai.