Hori Tupaea was born probably in 1879 or 1880 in the vicinity of Te Hauke, Hawke's Bay, the second child and eldest son of Arihi Te Nahu by her second marriage, to Hamiora Tupaea. Arihi was the eldest child of Karanama (Karanema) Te Nahu, who was in turn the eldest son of Ngati Te Whatuiapiti leader Te Hapuku and his senior wife, Te Heipora. Arihi, or Princess Alice, as she was known to Europeans, was thus of supreme rank. Through Te Hapuku and the ancestor, Te Huki, she had direct links to Kahungunu. One hapu important to her was Ngati Te Rangikoianake. Hori’s father was a younger son of the pre-eminent Tauranga chief Hori Kingi Tupaea of Ngai Te Rangi. His marriage to Arihi was arranged to repair the relations between Ngai Te Rangi and Ngati Kahungunu; his grandfather had been killed in the wars between them. Hori Tupaea was thus of supreme rank on both sides of his whakapapa.
Little is known of Hori Tupaea's childhood and education, but it is likely that he attended Te Aute College. Certainly he was part of a group of high-ranking young Anglicans who became the leaders of Ngati Kahungunu, and who were all disciples of Apirana Ngata in the Te Aute College Students' Association and later the Young Maori Party. He married Rauhina, about whom little has been recorded; they had no surviving children. They lived at Te Hauke with Hori's sister Makua-i-te-rangi Ellison and her family on a property once owned by Te Hapuku, and farmed family land at Opapa, near Lake Poukawa.
Tupaea emerged as a leader during the First World War, when he was involved in efforts to raise money for the projects of the Church Army of the Anglican Church, and for the Maori Soldiers' Fund of the Eastern Maori Patriotic Association. Tupaea was a member of the Tamatea Maori Council, a post he was to occupy for several years. With Paraire Tomoana and Taranaki Te Ua he represented the council in planning the grand event of March 1919 at Manutuke to welcome home the East Coast members of the New Zealand Maori (Pioneer) Battalion, and to raise money for the Maori Soldiers' Fund. Hori Tupaea was listed as a 'rising star' among the leaders there. In 1920 he was chairman of a general meeting at Te Hauke which endorsed Ngata's plans for the investment of the Maori Soldiers' Fund.
In 1921, with 26 other East Coast and Hawke's Bay leaders, he received a commemorative medal from the Prince of Wales. Tupaea was a member of the Heretaunga committee for the support of the Anglican Maori newspaper, Te Kopara. He was active in sport; in 1923 he was president of the Maori Hockey Club of central and southern Hawke's Bay.
Much of Hori Tupaea's energy was poured into the Anglican church. He campaigned for more financial support for the Waiapu diocese and Anglican Maori ministers. In 1925 he was the lay representative of Te Hauke to the district synod and was one of those pressing for a Maori bishopric. He called a meeting of the Waipatu parish at Te Hauke on 27 September 1925, invited the bishop of Waiapu, and asked that the Maori bishop be given the title of bishop of Te Aute and Aotearoa because of the contribution the college had made to the advancement of European education among the Maori people.
In December that year, representing Ngati Kahungunu and the Waiapu diocese as a layman, he attended a general synod of the Anglican church in Wellington; at that time the bill setting up a Maori bishopric was passed, and Hori Tupaea took part in the vigorous debate as to whether the new bishop should be a Maori or a Maori-speaking European. The bishops and Maori of the Auckland diocese wanted a Pakeha, but at the Wellington general synod of September 1926, Hori Tupaea and other Maori demanded that the bishop be Maori. Hori Tupaea said that in his opinion the Auckland Maori Anglicans were echoing the thoughts of the archbishop; this was confirmed when W. N. Panapa declared that Nga Puhi had been warned that if they insisted on a Maori, there would be no Maori bishopric. Frederick Bennett supported Panapa, but Tupaea said that if none of the existing Maori ministers were willing to serve, then Ngata, the other lay delegate from the Waiapu diocese, should be consecrated the first bishop. The debate ended when Ngata put a motion, seconded by Tupaea, that the first bishop be Maori; a counter motion that he be European was voted out. The motion was passed by a majority of only one, and consideration of the issue was postponed.
A district synod at Napier in October 1926 adopted Tupaea's suggestion that a standing committee be elected to assist the prospective Maori bishop. Eventually, Frederick Bennett, of Ngati Whakaue, was chosen as the first bishop of Aotearoa. In December 1928 he was consecrated at Pakipaki; Hori Tupaea was one of the three principal speakers.
Tupaea was also involved in local land and political matters; he held a hui at Te Hauke in July 1926 of all the owners of the low-lying Poukawa block near the lake. It was decided that the block should be drained, and the advice of the Native Trustee sought on the best way of preparing it for settlement. He served on a committee set up at Omahu in April 1927 to consider the effects of rating on Maori land. His committee discovered that the rating rolls were out of date, inaccurate, and had taken no account of subdivisions of blocks. They arranged, among other palliatives, that the Native Land Court would hear cases of outstanding rates and excessive rates demands.
Tupaea’s attention shifted to Napier land issues in the 1930s. In 1907, 1916 and 1919 Ngati Hinepare and Ngati Kahungunu had petitioned Parliament or applied to the Native Land Court to recognise and protect their fishing and other rights in Te Whanganui-a-Orotu, the Napier inner harbour, without success. They considered that the harbour had not been sold with the Ahuriri block in 1851. The Hawke’s Bay earthquake of 1931 raised the inner harbour, converting it into dry land, and it became even more urgent for the descendants of the owners of Ahuriri to press their claims, as the Napier Harbour Board claimed ownership and moved ahead with plans for the upraised land's development. In 1932, as the most senior living descendant of the owners, Hori Tupaea petitioned Parliament, asking for compensation for their right of property in the former inner harbour. A hearing was begun in the Native Land Court in April 1934; Hori's case was conducted by Raniera Ellison, his kinsman by marriage.
No report was completed in Hori Tupaea's lifetime, but further petitions eventually provoked its completion, and an inconclusive royal commission was held on the issue in 1948. The issue came before the Waitangi Tribunal in 1988, and a decision favourable to the Maori owners was reached in 1996.
In both church and lay affairs, Hori Tupaea was a tenacious advocate for his people. The satisfactory resolution of the dispute over the Maori bishopric, and the eventual settlement of the Napier harbour claim, owed much to his determination. In his last years he suffered from heart disease. He died in Waipukurau District Hospital on 1 April 1944, and was buried at Te Hauke.