Pātuki, of Ngāi Tahu, was born at Waipahi, Murihiku (South Otago/Southland), possibly as early as 1810 or as late as 1820, while his parents were returning to the Canterbury Plains area after a muttonbirding expedition. His mother was Te Wairua and his father was Henry Te Marama. Pātuki was descended on his mother's side from Te Wakatitiro and Rakiāmoa, and on his father's side from Whakakā, Taoka, and Ruahikihiki. He described his hapū as Ngāi Taoka and Ngāi Te Ruahikihiki. His maternal uncle was Tama-i-hara-nui, and he was also connected to Tūhawaiki, through his great-grandmother, Te Wakarawa, who was a sister to Honekai, Tūhawaiki's grandfather. Pātuki had at least two brothers, Te Ruruku and Henry Kurukuru, and a half-brother, John Williams Tohe (known as Bulla or Buller). Pātuki was baptised by the Reverend Charles Creed at Waikouaiti on 15 September 1844 as Hoani Raena (John Reynold) Pātuki. He was widely known as Tōpi (Toby) or Teone Tōpi (Johnny Toby).
Little is recorded of Pātuki's early life. As a youth he went to Foveaux Strait, probably about 1831, at the time Ngāti Toa besieged Kaiapoi pā. In late 1836 or early 1837 he was with Tūhawaiki in the attack on Ngāti Tama raiders at Tūtūrau and is credited with firing the shot which killed Ngāti Tama leader Te Pūoho-o-te-rangi. In 1838 he accompanied Tūhawaiki to Sydney, and soon after that took up whaling at William Stirling's station at Bluff. His ability was such that he was quickly promoted to headsman of his own boat. In 1844 on Ruapuke Island he assisted the newly arrived missionary, the Reverend J. F. H. Wohlers, by building the first mission house.
About 1840 Pātuki and Te Kawaunuhia (Te Kawainuhia) had a daughter, Erihāpeti Ngā Roimata, 'a most lovable child' in Wohlers's estimation. She died in October 1845. A second daughter, Ellen, died at about the age of six, in August 1850. Te Kawaunuhia had probably died before 1845. On 9 January 1853, at Ruapuke Island, Pātuki was married to Kate Kairo by the Reverend Wohlers. His name was recorded as John Toby Reynold Pātuki. Kate was baptised the same day. Because he had no sons, in 1856 Pātuki took another wife, Madeleine (Madeline) Kurukuru. She had been the wife of Tūhawaiki's son, John Frederick Kīhau, who drowned in February 1852; she had three children by this marriage. She and Pātuki had a son, Walter Tama-i-hara-nui, who was born at Ruapuke on 14 June 1856. Wohlers wrote that this liaison 'caused a vast deal of suffering to his lawful married wife Kate Kairo, the best and most beautiful Māori lady in the Straits, whom he sincerely loves'. Madeleine and Pātuki had four more children between 1858 and 1867: Johnston Reina, Morris Pātuki, John Maka Te Marama, and Kerekini (Gretchen) Reina. Kate Kairo died in November 1876, and in February 1881 the marriage between Pātuki and Madeleine Kurukuru was solemnised at Ruapuke.
When Tūhawaiki drowned near Tīmaru in 1844, Kīhau was regarded as his successor to the chieftainship of Murihiku. Kīhau was a shy youth of 14 and Pātuki became the effective leader on Ruapuke, where he was recognised as 'a young chief of rising influence', according to Edward Shortland. Shortland described Pātuki in 1843 as 'more European than…any New Zealander I have ever seen. He spoke very good English, was dressed in the style of the better class of English sailor, …and had the character of being one of the most expert whalers on the coast.' Wohlers characterised him in 1845 as 'a quiet friendly man and for that he is liked, but he has no authority over the natives'. By the late 1840s Pātuki could command only nominal influence over chiefs of lower rank. Nevertheless, from Kīhau's death in 1852 Pātuki was the acknowledged rangatira of Foveaux Strait.
Pātuki was a signatory to the sale of large blocks of Murihiku to John Jones and George Green in Sydney in 1838, and of further extensive areas in 1839, although most of these transactions were severely reduced or struck out by Colonel Edward Godfrey's land claims investigations in 1843. In 1844 Tūhawaiki signed the Otago deed as Pātuki's proxy, and Pātuki was a signatory to the Canterbury purchase in 1848 and the Murihiku sale in 1853, later disputing the reserves set aside.
Protracted dealings arose over the sale of Rakiura (Stewart Island). Unable to stem the influx of European settlers, Pātuki offered in 1860 to sell to the government all the land on the island west of Long. 168° excluding most of the east and north-east coasts. His position was compromised, however, by his involvement in the 'Gunpowder Plot' of 1861, when contraband gunpowder was landed at Paterson Inlet from an American vessel. Two Pākehā were fined by the Invercargill court but their penalties were later remitted when it became apparent that Pātuki was the effective instigator. He began to sell land to Australian immigrants, until in December 1863 the government passed the Stewart Island Annexation Act, which brought the island under the provincial administration of Southland. Negotiations followed which concluded, on 29 June 1864, with the sale of the whole island for £6,000. Pātuki received a reserve of 400 acres at Paterson Inlet, and an interest in £2,000 of the purchase price, which was invested at eight per cent for the heirs of Tūhawaiki.
In 1861 Pātuki spent a brief period goldmining at Gabriels Gully. He spent most of his later life on Ruapuke Island. He lived in a weatherboard house at Henrietta Bay and kept a few cattle and pigs. Wohlers observed that Pātuki's heart was never in farming, and like other Ruapuke chiefs he preferred riding, sailing, and muttonbirding. An expert in small craft, he owned a number of whaleboats, and had an interest in Tūhawaiki's schooner, the Perseverance, which was purchased in 1834. He also owned a cutter, the Levin (which sank in 1847), the Lady Grey and the Deveron.
From 1856 Pātuki was often in Invercargill, selling produce to the early settlers from a store in Esk Street. He also maintained an interest in horse-racing, and his mare won the Invercargill hack-hurdles in 1860. According to Wohlers his activities at home wavered 'between good intentions and loose habits'; one of the latter was his smuggling of liquor on to Ruapuke Island. He was instrumental in getting a school established on the island in 1868, and maintained a keen interest in education on Ruapuke and Rakiura. Living in 'proud poverty' near the end of his long life, he was a well-known and respected figure in Murihiku. He died on Ruapuke on 28 September 1900. His tangi was attended by many Māori and Pākehā, and a granite memorial was raised on his grave at Henrietta Bay.