Hēnare Kaihau was born probably between 1854 and 1860 at Waiuku, on the southern Manukau Harbour. He was the son of Ngāti Te Ata chief Aihepene (Ahipene) Kaihau, who also had tribal affiliations with Ngāti Urupikia, Ngāti Kahukōkā and Ngāti Tipā. Hēnare's mother's name was Rangipūkoru. Aihepene Kaihau was superintendent of police for the King movement rūnanga in 1858, and between 1862 and 1880 was a Native Department assessor at Waiuku. Little is known of Hēnare's personal life except that he married at least twice, and possibly six times, and from his second marriage had six daughters and two sons. His second wife, Louisa Flavell, also known as Maewa, was a composer to whom the words of the farewell song 'Haere rā', internationally known as 'Now is the hour', have been attributed.
Hēnare Kaihau attended Robert and Beatrice Maunsell's school at Kōhanga only briefly. He acquired a vast knowledge of tribal history and whakapapa, and later in Parliament he was to speak only in Māori. By his mid 20s he had become interested in Māori politics. He was associated with the Māori parliament movement, and was a staunch supporter of the King movement, becoming the principal adviser to Mahuta, the Māori King.
In 1884 and 1886 he stood unsuccessfully for Parliament in the Western Māori electorate. Success came in 1896 when, as the first candidate supported by the King movement, he was elected MHR for Western Māori. One of his first tasks in Parliament was to introduce in August 1898 the Māori Council Constitution Bill, which provided for a form of Māori self-government. A Māori council of 56 members would assume full power over Māori land and fishing grounds, supplanting the Native Land Court and settling all disputes relating to Māori land. The other Māori members of the House supported the principle of the bill but objected to the clause which stated that the mana of the council was to be vested in Mahuta for life and to descend to his lawful successors. The bill was discharged before its second reading.
Throughout his 15 years in Parliament Kaihau spoke on many issues concerning Māori people, always referring to the Treaty of Waitangi as a basis for their rights. The right to fish in traditional fishing grounds and to hunt native birds without restrictions must be preserved, he argued, for these foods were the staple diet of the Māori. He believed it important that Māori have a European-style education from properly trained teachers, and argued that they should then be given equal opportunity of employment in government departments.
He gave most of his attention, however, to the issue of Māori land. Deeply concerned about the effects of land confiscation in Waikato in particular, Kaihau lamented what he saw as unkept promises made by Premier Richard Seddon and Native Minister James Carroll to deal with this issue, and repeatedly reminded the government of this obligation. He argued vehemently against a number of the Māori land bills introduced into the House between 1897 and 1910. The most controversial of these was the Māori Lands Administration Bill, which was passed in October 1900. Kaihau at first believed that the bill would benefit Māori people by giving them greater control over their land, through the institution of district land councils. However, it soon became apparent that the act further restricted Māori initiative in dealing with their land, and he argued for its repeal.
In 1903 Kaihau took a seat on the Waikato District Māori Land Council, having been persuaded by James Carroll. But the results of the Māori Lands Administration Act 1900 and the unwillingness of the government to make land laws more equitable hardened him against future land legislation. He argued passionately that these laws were trampling Māori rights and mana that had been guaranteed to them under the Treaty of Waitangi. By 1910 these rights had effectively been taken away. Disillusioned and frustrated by the lack of commitment to Māori issues, by 1905 Kaihau spoke mostly to the Māori land bills and took his seat in Parliament only when such legislation was introduced. He did not speak in the House at all in 1906, 1908 and 1909.
During this period he turned his attention to the idea of re-establishing a Māori parliament, following the decline of the Kotahitanga movement of the 1890s. The new parliament was to be centred on Mahuta and his pā at Waahi. The aim was to rally all Māori leaders, devise a plan of self-determination and fight unjust land laws. Large meetings were held in 1907, but they failed to overcome divisions within the King movement and differences with tribes outside it.
In 1908 the Waikato leaders acted by themselves. Mahuta wanted to buy back confiscated land at Taupiri and Ngāruawahia where he would establish a township and parliament. Money was raised through the sale and lease of land. Some was invested by Kaihau in Auckland land companies and some placed in trust funds in Kaihau's name. By 1911 the companies had collapsed and over £50,000 of King movement money had been lost.
The failure of these investments coincided with charges of impropriety brought against Kaihau in Parliament. On 12 October 1910 John Hine, the member for Stratford, laid charges of corruption against several members. Kaihau was accused of having accepted money from electors for his work on petitions, and of receiving payment for setting up land sales: while he urged his people to hold on to their lands, he assisted those who were determined to sell. In his defence Kaihau stated that he had been working in the capacity of a licensed agent, and that lawyers and others in the House did similar work for their clients and constituents. He was found 'guilty of impropriety in the execution of his office'. The Speaker, however, observed that because 'the honourable member is a Native, and…does not speak our language', and 'our Standing Orders are not translated into the Māori language', he may not have been 'aware that he was doing what was improper.' No penalty was imposed.
In September 1911 Kaihau was granted 14 days' leave of absence from Parliament for health reasons; he had been suffering for some time from gout and rheumatic fever. Knowledge of his bad investments came to Mahuta just before the 1911 general election. Accusations had also been made that Kaihau had appropriated trust fund money for his own use. Mahuta subsequently transferred his allegiance to Māui Pōmare, and Pōmare defeated Kaihau at the election by 565 votes. Kaihau tried in 1919 to regain the seat, but without success. He died at Waiuku on 20 May the following year.
Hēnare Kaihau was a man of imposing presence. A large man (weighing 20 stone), he was 'a Hercules in strength and stature', in the words of the prime minister, William Massey, 'and a man with a very great deal of mental ability.' He was a master of political rhetoric, but was also described as 'extraordinarily good-natured and genial'. He has been remembered primarily for the loss of King movement money and the charge of political impropriety brought against him. However, these incidents should not overshadow his vision of Māori self-determination and his effort to unite the King and Kotahitanga movements to this end. His cry – 'give into the hands of the Māori people the power to administer their own affairs; cease to tie up the hands and feet of individuals owning the land' – should have been an important foundation for later demands for Māori self-determination.