In 1828, when Ngati Maru of Thames destroyed Otamataha pa at Te Papa, Tauranga, they left intact only the dwelling of the renowned and greatly feared tohunga Tahu. Nothing is known of Tahu's birth and parentage, but he was almost certainly from Ngai Tukairangi and Ngati Tapu, hapu of Ngai Te Rangi, who lived respectively at Otamataha pa and on the neighbouring land at Te Papa. Tahu became an inquirer after Christianity when he associated himself with the CMS mission station established by W. R. Wade at Te Papa in August 1835. From May 1836 to January 1838 the station was cared for by missionaries who, because of the war between Ngai Te Rangi and Te Arawa, did not have their families with them. Tahu assisted these missionaries. As one of the owners of the land on which the mission stood, he signed the deeds of conveyance of the land to the missionary A. N. Brown (acting on behalf of the CMS), in two lots, in 1838 and 1839.
On Good Friday, 29 March 1839, Tahu was baptised by Brown, taking the names Matiu Parakatone. In a remarkable gesture Matiu Tahu publicly renounced his powers as tohunga by placing on his head a vessel in which food had been cooked. He moved soon after to Otumoetai pa, where he worked as a mission teacher until the early 1850s, when he and his wife, Makareta Aneta Poho, shifted to Ohuki. Confirmed by Bishop G. A. Selwyn on 30 March 1846, he became Brown's most trusted teacher. Matiu Tahu accompanied Brown on missionary visits to Taupo in 1841 and to Ruatoki in 1846; and on his own missionary journeys he travelled to Thames in 1842 and Matamata in 1849. In April 1851 he accompanied Brown and a large party of Ngai Te Rangi, led by Hori Kingi Tupaea, to Thames to make peace with Ngati Maru. There, on Sunday 12 April, he preached to the assembled tribes from John 17:12. On these journeys Matiu Tahu and Brown often discussed the state of the country and compared Maori and English characteristics and customs, as on an 1846 trip: ' "You are not satisfied with us", remarked the old man [Matiu], "and you often express a fear that our religion is only lip service, that it has no root in our hearts. You forget what we were and what we have thrown away – our cannibalism, our murders, our infanticide, our Tapus, which were Gods to us. What prevents our return to these things but Religion?" '
Matiu Tahu was a leading spokesman of his people. He gave sound advice to Brown during political crises such as the 1852 dispute with Te Arawa over Motiti Island. Well versed in the traditions of the Maori, he spoke freely about them to the missionaries W. R. Wade, A. N. Brown and J. A. Wilson, and to visitors such as the missionary William Colenso and Lady Mary Martin, all of whom recorded something of their conversations with him. Wilson described him in 1837 as 'a short, strong built man of about 45 years of age, round headed and rather bald; his face plain, good natured and intelligent'. Lady Martin found him a gentleman in 'manner, thought and action', and CMS missionary William Williams remembered him as 'full of life and energy'.
Matiu Tahu died at Ohuki, Tauranga, in late 1863 or early 1864. He left no family; his wife had predeceased him by a week or two, and his adopted daughter, Harete Paraone (named after Charlotte Brown), of whom he was very fond, had died in 1847. Matiu Tahu had been an invaluable support to Brown for nearly 25 years. Brown acknowledged this in a generous tribute to the 'good old man', who had been 'most indefatigable in instructing his countrymen'.