Hori Kerei Taiaroa was born at Otakou, on the Otago peninsula, probably in the 1830s or early 1840s. His father was the prominent Ngai Tahu chief Te Matenga Taiaroa, of Ngai Te Ruahikihiki, and his mother was Mawera of Ngati Rangi-whakaputa. The only surviving son, he was named Huriwhenua in commemoration of a traditional peacemaking between Ngai Tahu and Te Ati Awa in 1844, when Te Maraini Huriwhenua of Te Ati Awa visited Otakou. He was christened Hori Kerei about 1858 or 1859 after former governor Sir George Grey. Older Ngai Tahu continued to call him Huriwhenua.
Taiaroa grew up at Otakou, where he was taught to read and write by a European mission teacher of the Wesleyan church, of which his father had become a supporter. In the late 1850s or sometime in the 1860s, at Otakou, he married Tini Pana (Jane Burns), whose mother was of Ngai Tuahuriri of Ngai Tahu, and whose Scottish father was a farmer at Moeraki.
In February 1862 Te Matenga Taiaroa dictated a testament 'To all my tribe, to my hapu, and to my son', exhorting them to see that the promises made by William Wakefield, H. T. Kemp and W. B. D. Mantell when purchasing Ngai Tahu lands were carried out. He urged them also to acknowledge the Queen's sovereignty and to treat Europeans well. Hori Kerei Taiaroa made the fulfilment of this testament his life's work.
In May 1868, when the Native Land Court first sat at Dunedin, Taiaroa and Timoti Karetai applied for an investigation of the former Maori reserve in Princes Street, Dunedin, which the government had granted to the province of Otago together with over £6,000 in rents which were supposed to have been held in trust by the government for Ngai Tahu. The court declared it a matter for the Supreme Court. Subsequently, the Court of Appeal in November 1869 ruled in favour of the Otago province, and Taiaroa and Topi Patuki initiated an appeal to the Privy Council.
In February 1871 Taiaroa was elected to the House of Representatives as member for Southern Maori. This he saw as a means to fulfil his father's behest. Ngai Tahu claims had been first brought to public and official notice in 1849 by the Ngai Tuahuriri chief Matiaha Tiramorehu. Tiramorehu had called for adequate pastoral lands to be reserved for Ngai Tahu under the terms of Kemp's purchase of 1848, and had sought a revision of Grey's Wairau purchase of 1847 which had recognised Ngati Toa's claim to Kaiapoi and Ngai Tahu territory to the north. Taiaroa adopted a more southern emphasis for the Ngai Tahu claims, in keeping with his father's conciliatory attitude towards Ngati Toa.
In Parliament Taiaroa spoke on a wide range of issues, particularly those affecting Maori, but he made the Ngai Tahu claims his main business. In November 1871 he successfully moved that copies of the South Island land purchase deeds be printed. In August 1872 he secured the passage of a motion that the promises in Kemp's deed should be carried out, and he initiated the setting up in July that year of a committee of the House to examine 'unfulfilled promises to Natives in the Middle Island.' The committee, which included the native minister, Donald McLean, found that the claims of Ngai Tahu had not received the attention they deserved, and recommended the appointment of an impartial commission 'as a Court of equity and good conscience'. Although the recommendation was not acted on, Taiaroa had achieved the important step of getting the Ngai Tahu claims into the formal business of Parliament.
In November 1872 the Otago provincial government offered Ngai Tahu £5,000 to withdraw their Privy Council case and surrender all claim to the Princes Street reserve. Taiaroa agreed to this compromise. In January 1874 Taiaroa and Patuki each received £1,000 of this money, and the rest was distributed in Otago, Canterbury and Murihiku (South Otago–Southland). Taiaroa then applied to McLean for the £6,000 in rents, with interest; not until 1880 would this compensation be paid.
Taiaroa now sought tribal support and financial backing for his work on the Ngai Tahu claims, and absolute control of the fund which was to be canvassed from the tribe. A meeting of Ngai Tahu and Ngati Mamoe chiefs was convened at Otakou marae on 4 June 1875 and a parchment was produced for their signature. By this 'Covenant' Taiaroa was to be given sole charge of the campaign, with authority to appoint lawyers, sole control of funds and complete discretion over expenditure. Sixty-three signed. Taiaroa afterwards claimed that these sweeping powers were conferred on him by 'the whole of the Ngai Tahu'; however, a number of prominent Ngai Tahu leaders did not sign the covenant. Taiaroa's support came predominantly from Otakou and Murihiku: relatively few of the covenant's signatories were from north of Otakou.
On 14 July 1874 Mantell wrote to Taiaroa, after some prompting from Taiaroa himself, stating that at the time of the Murihiku purchase (1853) he had privately promised Te Matenga Taiaroa a personal reserve of 100 acres at Anita Bay, Milford Sound, the well-known source of bowenite greenstone. On the strength of Mantell's statement, Hori Kerei Taiaroa for the rest of his life claimed personal title to the whole bowenite resource at Milford.
Ngai Tahu at this time had a staunch ally in Alexander Mackay, the commissioner of native reserves. Ngai Tahu's original title to Kemp's block was being questioned on the grounds that 20 million acres was too vast an area to have been occupied by Maori. Mackay reported to Parliament that the Ngai Tahu customary title to the land was 'good on all three grounds' of heredity, conquest and occupation. He also declared that at Otago, Ngai Tahu should have received the New Zealand Company tenths, with a calculated value of £29,920, plus interest. Taiaroa suggested that the government pay Ngai Tahu £2 million as compensation, a figure Mackay thought too extravagant for the government to consider. In October 1876 Taiaroa issued a trenchant reply to Chief Judge F. D. Fenton, who had criticised as unfounded a Ngai Tahu petition regarding the Otago purchase, Kemp's Purchase, and the Native Land Court hearings of 1868 (at which Fenton had presided).
By the end of 1877 Taiaroa had banked some £3,000 collected from Ngai Tahu. He moved an amendment to the Crown Redress Act 1871 to enable the claim to be taken to the Supreme Court. In October the Atkinson ministry lost office. The native minister in the new government, John Sheehan, had more sympathy than his predecessor, Donald McLean, for an inquiry into Maori land purchases of the kind Taiaroa was seeking.
In the winter of that year the visionary religious leader Hipa Te Maiharoa of Arowhenua, assisted by Horomona Pohio, led over 100 people to Te Ao Marama (near Omarama) where they occupied a settler's leasehold land to reaffirm the Ngai Tahu claim to the interior of the South Island. Taiaroa saw this action as a threat to his leadership and to his attempts to win the sympathy of the government for the setting up of a commission of inquiry. In October 1878 Pohio went to Wellington, where Taiaroa arranged an interview with Sheehan. The following month Taiaroa accompanied the native minister to Te Ao Marama to try to persuade the people to leave, but without success.
The Grey government agreed to pay Ngai Tahu £5,000 as compensation for the back-rents from the Princes Street reserve in December 1877, and in June 1878 £1,000 was paid to Ngai Tahu claimants assembled at Kaiapoi. Two years later Taiaroa and Patuki accepted the other £4,000. Although the Legislative Council in 1885 cleared Taiaroa of any improper action in regard to this money, the belief continued at Otakou that he did not distribute it properly.
In 1878 Taiaroa and his family moved to a large new house, Te Awhitu, which he had had built at Taumutu, one of his father's ancestral places. There, when Parliament was not in session, he lived the life of a country gentleman. In February 1879 he was called to the Legislative Council. A commission consisting of T. H. Smith and F. E. Nairn was appointed to inquire into the Otago, Kemp's block, Murihiku and Akaroa purchases. In April, on the eve of the commission's hearings, at the government's request Taiaroa travelled again to Te Ao Marama with Topi Patuki and Rawiri Te Mamaru to try to persuade Te Maiharoa and Pohio to leave and await the outcome of the Smith–Nairn commission. He was again unsuccessful, and the people were later evicted by armed police. Taiaroa appointed the legal firm of Izard and Bell to assist him at the Smith–Nairn commission's hearings, which extended over a period of 12 months. While the commission was sitting, the fall of the Grey ministry brought John Bryce to office as minister for native affairs, and he refused to extend the commission's funding to enable it to complete its work. Its interim report was sympathetic to the Ngai Tahu claim, but the report was eventually rejected by the government. The commission had taken detailed evidence from many Maori witnesses who had been present at the land purchases, and this, together with the detailed record of mahinga kai (places where food was produced or procured) and the associated kainga nohoanga (seasonal settlements) which Taiaroa collated from meetings of elders, constituted a priceless record of the Ngai Tahu view of the land purchases and of their traditional way of life. It was perhaps Hori Kerei Taiaroa's most lasting achievement.
In the Legislative Council on 20 July 1880 Taiaroa attempted to criticise the government's policy on the appointment of native assessors. In response the attorney general, Frederick Whitaker, drew attention to the fact that any salaried government official was disqualified by law from sitting in the Council and claimed that Taiaroa had never formally resigned his own assessorship. Taiaroa thereupon ceased to attend the Council, although he denied either having drawn any pay since taking his seat or knowing that he was technically disqualified. On 25 August the Council resolved to disqualify him formally. Several members defended Taiaroa's personal integrity, and it was noted that when three European members of the House of Representatives had been similarly disqualified, they were immediately indemnified. The case aroused much bitterness and resentment among Maori around the country, and was a bitter blow to Taiaroa. The MHR for Southern Maori, Ihaia Tainui, resigned to allow him to be re-elected to this seat. Taiaroa resigned his assessorship in January 1881.
In May 1885 Taiaroa was again called to the Legislative Council, where he remained until his death. He continued to press the government for recognition of the Ngai Tahu claims. In 1886 John Ballance, as native minister, agreed to the appointment of Judge Alexander Mackay as commissioner to report 'on the Middle Island Native Land Question'. In 1887 Mackay reported that 186,112 acres of additional land were required to provide adequately for Ngai Tahu in the Murihiku and Kemp blocks, including Banks Peninsula. The following year the Atkinson ministry set up a joint parliamentary committee to 'bring about a final settlement', but Taiaroa was not included, although he was called on to give evidence. The committee recommended a further inquiry.
In 1890 Mackay was appointed commissioner to ascertain the degree of landlessness among Ngai Tahu. He reported that 46 per cent of Ngai Tahu had insufficient land for their support and 44 per cent had none. Taiaroa and Tame Parata, MHR for Southern Maori, continued in Parliament to press the government for some action, and in the recess of 1892–93 they accompanied the native minister, A. J. Cadman, when he toured Ngai Tahu settlements. Cadman proposed allocating 90,466 acres, mainly remote bushland in western Southland and Stewart Island. Taiaroa announced in the Legislative Council that Ngai Tahu would accept this land, but not in settlement of their claims, as the land was considered practically worthless for settlement. The government finally awarded this land to Ngai Tahu the year after Taiaroa's death, under the South Island Landless Natives Act 1906.
After W. B. D. Mantell's death in 1895 Taiaroa claimed that Mantell's promise to his father of a reserve at Anita Bay was for 'at least 1,000 acres', not 100, and he asked the premier, Richard Seddon, for land to be awarded to him in some other locality. He claimed to Seddon that he had been a party to the Murihiku purchase, although some years earlier he had strongly denied this, stating that his mark on one of the receipts, written when he was a boy, had been forged. The government in 1898 agreed to grant Taiaroa only the 100 acres at Anita Bay as a final settlement. Eventually, two years after Taiaroa's death, an inquiry by two judges of the Native Land Court ruled the family's claim for £5,000 in compensation to be unfounded, but recommended that £53 be paid 'as an act of grace'. In 1909 Hori Kerei's sons Te Oti and Riki accepted this money on the family's behalf.
To Hori Kerei Taiaroa the Ngai Tahu claims were a matter of family mana as well as justice for his tribe. He revived his father's dubious claim to be paramount chief of Ngai Tahu. In keeping with his father's testament he concentrated on claims arising from the three purchases to which his father had been a signatory – the Otago purchase of 1844, Kemp's purchase of 1848 and the Murihiku purchase of 1853 – and also the Akaroa purchase of 1856 in which Ngai Te Ruahikihiki had a customary interest. Taiaroa showed little interest in claims arising from the Port Cooper, Port Levy, North Canterbury, Kaikoura and Arahura purchases, which affected hapu in which he had few connections. He at times incurred displeasure from other Ngai Tahu for siding with the government against them.
Taiaroa took an important role in wider Maori politics. He attended many meetings around the country, particularly those of Te Kotahitanga. In 1893 he presented a bill to the Kotahitanga parliament, asking for power of assembly for the Maori parliament, but not separate Maori government. The debate over this and a more radical bill presented by Hone Heke created a rift within the Kotahitanga movement which was never resolved.
By his Maori contemporaries Taiaroa was regarded as a competent and pragmatic politician. As an MHR he was often praised for his outspoken criticism of the government. However, after his appointment to the Legislative Council he was regarded with suspicion by some as becoming pro-government. In political life his reputation suffered from a tendency to overstate his case and at times contradict himself, especially regarding his own and his father's affairs. He did not stand up well under hostile cross-examination on the claims, and his financial dealings were sometimes viewed with suspicion. But he vigorously advanced the Ngai Tahu cause in Parliament in an often lonely battle against impossible odds. In the nature of colonial politics his efforts were doomed to failure, and in the last decade of his life, in failing health, he saw his hopes of a parliamentary settlement of the Ngai Tahu claims disappointed.
Hori Kerei Taiaroa died at Wellington on 4 August 1905. He was buried in the churchyard at Otakou. He was survived by his wife, Tini, and four sons, Te One Wiwi, Te Oti Kerei, Riki Te Mairaki and Hoani Korako. Two sons, Matenga Kerei (Te Maateka) and Apa, had died before him.