Tamihana Te Rauparaha, known also as Katu, was the son of the great Ngati Toa leader Te Rauparaha and his fifth and senior wife, Te Akau of Tuhourangi. He was born at Pukearuhe, a Ngati Tama pa in northern Taranaki, while Ngati Toa were on their long journey from Kawhia to the south. He took the name Tamihana (Thompson) when he was baptised by CMS missionary Octavius Hadfield on 21 March 1841, and was known from that time on as Tamihana. On 11 September 1843 he and Ruta (Ruth) Te Kapu, daughter of Tawhiri of Ngati Raukawa, were married at Otaki by Hadfield.
Katu was carried as a baby to Kapiti, the island which became the new home of Ngati Toa. As a child he accompanied his father on war expeditions. On one occasion, while making cartridges, he injured himself and others by throwing gunpowder into a campfire. He was at the storming of Kaiapoi pa in 1831 and was with his father when they were ambushed by Ngai Tahu at Kapara-te-hau (Lake Grassmere), about 1833. Tamihana subsequently wrote down accounts of these and other Ngati Toa campaigns, putting together information he had gathered from Te Rauparaha. These writings have been used extensively by historians.
Christianity was brought to Kapiti, and also to Otaki where Katu was living, by Maori who had been taken as captives to the Bay of Islands and released when their masters became Christian. In November 1839 he and his cousin Matene Te Whiwhi went by ship to the Bay of Islands to seek a missionary for the Kapiti area. They returned with Henry Williams and Octavius Hadfield; Hadfield remained permanently on the Kapiti coast. In 1843 Tamihana and Te Whiwhi went to the South Island and preached Christianity to their relations there and to Ngai Tahu, their former enemies. When he was asked by Ngai Tahu chiefs if his father was going to come to attack them he would reply, 'He indeed will not come; for I have indeed come hither to you to bring an end to war-fare, and to bind firmly peace by virtue of the words of the Gospel of the Lord.' The next year he accompanied Bishop G. A. Selwyn on his first overland trek in the South Island, which began with the first church service in South Canterbury, at Te Wai-a-te-ruati. In these ways Tamihana helped to bring the fighting to an end, and to bring Christianity to the southern parts of New Zealand.
In 1845 he was sent by his father to the Hutt Valley in an effort to make sure that Maori left the land which was in dispute with settlers, as Te Rauparaha and Te Rangihaeata had agreed. He attended St John's College in Auckland and was there in 1846 when his father was arrested on the orders of Governor George Grey. He visited his father on board the Calliope and quotes his father as saying, 'Oh son! both you and Matene [Te Whiwhi], go to your people! and say: repay only with goodness on my account; do not incurr ill-will with the Europeans on my account – for only by Goodwill is the salvation of Man, Woman and Child.' Tamihana took this message to Otaki, where Ngati Raukawa were planning to take revenge for the arrest of Te Rauparaha, by joining with Te Rangihaeata to attack Wellington. They were dissuaded from war by Te Rauparaha's words. During Te Rauparaha's detention in Auckland Tamihana and other Ngati Toa leaders agreed to sell the Wairau plains to the government for £3,000. When Te Rauparaha was released in January 1848, Tamihana was at Otaki to welcome him.
Tamihana was one of the young chiefs of Otaki who adopted the clothing and lifestyle of an English gentleman. He lived in a European-style house and had European servants. He became a successful sheepfarmer and a man of considerable wealth; by 1866 he had a flock of 700 sheep. He owned land in the Otaki and Foxton districts; he is said to have lived the life of a country gentleman.
On 19 December 1850 Tamihana left for England, on the Wesleyan Missionary Society vessel John Wesley, together with Jane and William Williams, other missionaries and members of their families. They arrived in April 1851. On 30 June 1852 Tamihana was presented to Queen Victoria. Later in the same year he returned to New Zealand. He now sought to establish a monarchy for the Maori people, to give them a unity beyond that of the tribe and to bring law and security to their land. Potatau Te Wherowhero of Ngati Mahuta eventually agreed to become king and was installed at Ngaruawahia in 1858. Tamihana supported the King movement's attempt to halt the sale of Maori land. He wanted to put a limit to further European encroachment so that the two races could live peacefully side by side.
When supporters of the King joined Wiremu Kingi Te Rangitake of Te Ati Awa in his resistance to the government over the land purchase at Waitara in 1860, Tamihana broke with the movement. In May 1860 he opposed the raising of the King's flag at Otaki. He went from there to Papawai to oppose King influence in Wairarapa. In a letter to Bishop Selwyn on 19 April 1860 he wrote that he was living in fear that the Taranaki war would spread south to Otaki; he wanted Maori and Pakeha to live in peace, health and goodwill. In the later 1860s Tamihana and Te Whiwhi used their influence to prevent the wars from reaching the Wellington area. They gained acceptance for the proposal that it should be a zone of peace, although men would be able to travel from it to join the fighting in the north, if they wished.
In 1866 Tamihana supported the sale of the Rangitikei–Manawatu block against the objections of some Ngati Raukawa supporters of the King living there. The sale was supported by Ngati Toa, as well as by the tribes who had lived there before the northern invasions. In spite of Ngati Raukawa's claim that it was theirs by conquest and occupation, it was sold to the government for £25,000. In 1869 Tamihana accompanied the governor, G. F. Bowen, on a tour of the South Island with Wi Tako Ngatata and Mete Kingi Te Rangi Paetahi. By 1864 Tamihana held the position of senior assessor and received an annual salary of £100.
Tamihana Te Rauparaha died on 22 or 23 October 1876, at the age of 57 according to one obituary. He is said to be buried in an unmarked grave at Otaki, beside his wife, who had died in 1870. They had had no children, but had an adopted son, Wiremu Kerei Kupapa.