Tāmihana Te Rauparaha, known also as Katu, was the son of the great Ngāti Toa leader Te Rauparaha and his fifth and senior wife, Te Ākau of Tūhourangi. He was born at Pukearuhe, a Ngāti Tama pā in northern Taranaki, while Ngāti Toa were on their long journey from Kāwhia to the south. He took the name Tāmihana (Thompson) when he was baptised by CMS missionary Octavius Hadfield on 21 March 1841, and was known from that time on as Tāmihana. On 11 September 1843 he and Ruta (Ruth) Te Kapu, daughter of Tāwhiri of Ngāti Raukawa, were married at Ōtaki by Hadfield.
Katu was carried as a baby to Kāpiti, the island which became the new home of Ngāti 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 pā in 1831 and was with his father when they were ambushed by Ngāi Tahu at Kāparatehau (Lake Grassmere), about 1833. Tāmihana subsequently wrote down accounts of these and other Ngāti Toa campaigns, putting together information he had gathered from Te Rauparaha. These writings have been used extensively by historians.
Christianity was brought to Kāpiti, and also to Ōtaki where Katu was living, by Māori 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 Mātene Te Whiwhi went by ship to the Bay of Islands to seek a missionary for the Kāpiti area. They returned with Henry Williams and Octavius Hadfield; Hadfield remained permanently on the Kāpiti coast. In 1843 Tāmihana and Te Whiwhi went to the South Island and preached Christianity to their relations there and to Ngāi Tahu, their former enemies. When he was asked by Ngāi 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 Ruatī. In these ways Tāmihana 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 Māori 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 Mātene [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.' Tāmihana took this message to Ōtaki, where Ngāti 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 Tāmihana and other Ngāti Toa leaders agreed to sell the Wairau plains to the government for £3,000. When Te Rauparaha was released in January 1848, Tāmihana was at Ōtaki to welcome him.
Tāmihana was one of the young chiefs of Ōtaki 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 Ōtaki and Foxton districts; he is said to have lived the life of a country gentleman.
On 19 December 1850 Tāmihana 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 Tāmihana was presented to Queen Victoria. Later in the same year he returned to New Zealand. He now sought to establish a monarchy for the Māori people, to give them a unity beyond that of the tribe and to bring law and security to their land. Pōtatau Te Wherowhero of Ngāti Mahuta eventually agreed to become king and was installed at Ngāruawāhia in 1858. Tāmihana supported the King movement's attempt to halt the sale of Māori 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 Kīngi Te Rangitāke of Te Āti Awa in his resistance to the government over the land purchase at Waitara in 1860, Tāmihana broke with the movement. In May 1860 he opposed the raising of the King's flag at Ōtaki. He went from there to Pāpāwai 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 Ōtaki; he wanted Māori and Pākehā to live in peace, health and goodwill. In the later 1860s Tāmihana 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 Tāmihana supported the sale of the Rangitīkei–Manawatū block against the objections of some Ngāti Raukawa supporters of the King living there. The sale was supported by Ngāti Toa, as well as by the tribes who had lived there before the northern invasions. In spite of Ngāti Raukawa's claim that it was theirs by conquest and occupation, it was sold to the government for £25,000. In 1869 Tāmihana accompanied the governor, G. F. Bowen, on a tour of the South Island with Wī Tako Ngātata and Mete Kīngi Te Rangi Paetahi. By 1864 Tāmihana held the position of senior assessor and received an annual salary of £100.
Tāmihana 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 Ōtaki, beside his wife, who had died in 1870. They had had no children, but had an adopted son, Wiremu Kerei Kūpapa.