Tareahi was born late in the eighteenth century, probably at Te Poraiti, Wharerangi, on the western shores of Te Whanganui-a-Orotu, the inner harbour of present day Napier. As a Ngati Kahungunu leader, Tareahi inherited his ancestral rights in this district from his mother, Te Huripatu, of Ngati Hinepare. His father, Waitaringa, belonged to Ngai Takaha, a hapu who lived under the mana of Ngati Te Upokoiri, on the upper Ngaruroro River.
In the turbulent period between 1800 and 1830 the tribes of Heretaunga (Hawke's Bay) were either at war with one another or fighting off invaders. In this situation Tareahi developed his warlike character. Because of his fighting qualities he shared the leadership of Ngati Hinepare with more senior men, Haemania and Pakapaka, the sons of Tarewai. However, some time before 1820 Pakapaka was killed at the battle of Pukemokimoki, on the south side of Ahuriri hill (in present day Napier); he was leading his people against Ngati Parau. As Pakapaka's elder brother, Haemania, was already dead, it was left to Tareahi to avenge this killing. He did so at the battle of Taitimuroa. Before the battle Tareahi feigned a retreat around a bend of the Tutaekuri River and stopped to plan his tactics. First he sang a lament for Pakapaka to assuage his grief and rally his warriors. Then he told the Ngati Hinepare fighting men to advance under cover of darkness and set fire to the enemy canoes. At the same time the Ngati Te Upokoiri warriors approached Pukemokimoki pa from the opposite side. The blazing canoes drew the defenders from the pa, and Tareahi attacked. Many were killed, Pakapaka's death was avenged, and Tareahi was recognised as the principal leader of Ngati Hinepare.
In the 1820s, when northern invaders were threatening Ahuriri, Te Pareihe, the leader of Ngati Te Whatu-i-apiti, withdrew his followers to Nukutaurua, on the Mahia peninsula. Tareahi, however, remained to support Te Hauwaho of Ngati Parau. Together they set about strengthening their island fortress, Te Pakake. But, in the battle fought there in the early 1820s, they were no match for the muskets and numbers of Waikato, Ngati Tuwharetoa, Ngati Maniapoto and Ngati Raukawa. There was a massacre and Te Hauwaho was killed. But Tareahi was spared and the prisoners, gathering around him, mingled their tears. Tareahi sang a lament, and urged them to make for his cultivations at Matahourua if they managed to escape. The prisoners, including Tareahi, were taken to the Waikato district, however. Waikato leader Te Wherowhero wept when they arrived, for he knew that the Heretaunga people had been slaughtered without sufficient cause, and he helped to arrange their return. Paora Kaiwhata, who was with Tareahi, his father, said that they were away for 18 months.
When Tareahi returned, he found the country deserted. He did not, however, join his people at the refuge on the Mahia peninsula, but lived on his land near Lake Oingo. Thus he kept the fires of Ngati Hinepare and Ngati Te Upokoiri alight on their lands, and instructed Paora in the history and customs of the tribe.
Tareahi had several children. His first son, Porokoru Mapu, was born to Hine-whaka-ehua of Ngati Kopua. A daughter, Hepora, was born to Tareahi and the sister of Hine-whaka-ehua, Whakahiahia. Tareahi's third wife, Whareunga, of Ngati Mahu, had three children: Ani Kanara Marewa, who married Papaka, younger brother of Mananui and Iwikau Te Heuheu Tukino; Rawinia Kaingaroa, who married Pakapaka's grandson; and Paora Kaiwhata, who was the last tattooed chief of Ngati Hinepare.
In an era in which few war leaders lived to old age, Tareahi was unusual. He survived to see peace concluded with Ngati Tuwharetoa, the return of his people to their lands, the coming of Christianity to Heretaunga in the 1840s, and the purchase of the Ahuriri block by the government in 1851.
Tareahi was baptised by the missionary William Colenso in the late 1840s. He took the name Rawiri, a fitting name for one who, like the psalmist David, was a great warrior and a poet. In 1850 Colenso visited him at Te Poraiti; he found him busy at work making ropes for his fishing nets. Tareahi asked Colenso to baptise the children of the pa, and told the missionary that he always prayed at morning and evening, even when he was alone. Tareahi warned Colenso of hardships ahead. 'Be patient', he said, 'endure hardness'. He may well have anticipated the condemnation that was soon to fall on Colenso for his liaison with a Maori woman.
Donald McLean, at that time a government agent investigating land purchases, met Tareahi in December 1850 at Wharerangi. 'Old Rawiri, a legendary fixture[,] resides there', he wrote. 'He, his son and wives are now reciting; one of the old men, like the prophet of old, leaning on his staff.'
Rawiri Tareahi spent his declining days at Te Poraiti pa. He died there, possibly in the 1850s. According to his dying wish, he was buried by his sons within the sound of the sea, below Te Poraiti.