Ruatara was one of the first Ngāpuhi leaders to become closely associated with Europeans. For most of his life he lived in the vicinity of Te Puna, in the Bay of Islands. His date of birth is uncertain and his parentage is debated. According to Samuel Marsden, chaplain of New South Wales, Ruatara was about 22 in 1809. Marsden was also under the impression that Ruatara's father was Kaparu, younger brother of the chief Te Pahi, while his mother was the sister of Hongi Hika. But more recent research suggests that his father was Te Aweawe of Ngāti Rāhiri and Ngāti Tautahi sections of Ngāpuhi, and his mother Tauramoko, of Ngāti Rāhiri and Ngāti Hineira. Ruatara was probably related to Ngāti Rēhia too. His second wife was Rahu, whose sister married the chief Waikato, of Te Hikutū. Te Hikutū people came to live at Rangihoua after the marriage of Ruatara and Rahu.
Ruatara left New Zealand in 1805, as a crewmember on the whaling ship Argo. His motive, apparently, was to see George III. He was to spend most of the next four years serving on various whaling ships. Some ships' masters treated him well, while others defrauded and abandoned him. He suffered starvation and beatings. In 1809 Marsden, after a visit to England, was returning to Australia by the Ann, a convict vessel, when he discovered Ruatara. The chief was ill and neglected, vomiting blood because of the severity of his previous shipmates' beatings. He was also disconsolate because, although he had finally reached England, he had not been permitted to land and see the King. Marsden ensured that Ruatara was cared for and supplied with clothes, and, when the Ann reached Port Jackson (Sydney), invited him to his home at Parramatta.
Ruatara spent eight months with Marsden. He conceived a grand plan to introduce wheat production to New Zealand, which would provide his people with a valuable food source and an export crop. He studied European agricultural techniques, carpentry and other skills, and, when Marsden arranged a passage for him to New Zealand in the whaling ship Frederick, he took with him tools and a quantity of seed wheat. Once again he was defrauded and abandoned, this time on Norfolk Island. Rescued by the whaling ship Ann, he was taken back to Port Jackson and did not finally reach home until about 1812.
On arrival at Rangihoua, Ruatara found that tribal fortunes had changed. Te Puna, the island of Te Pahi, senior chief of Te Puna and Rangihoua, had been attacked by vengeful European whalers, who had killed many of the inhabitants. Te Pahi had survived but died shortly after. He had been held responsible for the massacre of the Boyd's crew at Whangaroa in 1809. Te Pahi's presumptive heir, 'Ogateeree' (Hokatiri?), had disappeared, presumably killed in the attack on Te Puna; and the next heir, Te Uri-o-Kanae, seems to have been incapable of leadership. Ruatara was recognised as the successor to Te Pahi's mana. It was probably at this time that he took his second wife, Rahu, and his third wife; his first wife was Miki, daughter of Waraki of Ngāti Rāhiri. Rahu, the widow of a chief killed in battle, seems to have been regarded as his senior wife; she gave birth to their son in 1814.
Ruatara's position as successor to Te Pahi was still open to challenge. He was very young; his wealth in the form of tools, clothes and weapons brought him much respect, but his stories of strange marvels in foreign places provoked some incredulity and ridicule. On his return he had immediately set about distributing seed wheat, but Māori were used to root rather than grain crops, and many refused to believe in its value. He was not able to prove his assertion that bread and biscuits could be made from the new crop until 1814. In that year Marsden purchased the Active, and sent Thomas Kendall and others to consult about setting up a Church Missionary Society mission. Marsden sent Ruatara many gifts, including a hand-powered flour mill; he was at last able to convince his fellow chiefs of the value of wheat. Marsden had also sent seed wheat, and Ruatara distributed it to the most important chiefs; wheat production was under way.
Ruatara accompanied the Active when it returned to Port Jackson, despite the opposition of his people. He spent some five months in further study of European agricultural techniques and other skills, and in acquiring more tools and weapons. He was given gifts by the governor of New South Wales, Lachlan Macquarie, and others who were anxious to smooth the path of the projected mission. These gifts included a mare, a cow and other livestock, and a military uniform. In addition the missionary party brought to New Zealand poultry, seed and seedlings of many useful plants.
Arriving at the Bay of Islands on 22 December 1814, Ruatara showed his determination to protect his Pākehā, the first CMS missionaries, Thomas Kendall, John King and William Hall. He warned them of dangers, took great personal risks in helping them to establish friendly relations with the people of North Cape and Whangaroa, and helped them to build houses at Rangihoua, where they were to live under his protection. He escorted Marsden, who had been on the Active, to the Thames–Hauraki area, again at some risk to himself. Yet by now Ruatara entertained serious doubts as to the intentions of the missionaries. He had been warned in Port Jackson that they were merely the forerunners of settlers and soldiers, who would take the country and reduce the Māori to the wretched condition of the Australian Aborigines which he himself had seen. Marsden had reassured him by offering to turn back the Active, but Ruatara was never completely sure of the wisdom of allowing the missionaries to settle. His aid was sometimes perfunctory, and he demanded payment for the land and the many services required by the missionaries.
Ruatara, however, put his doubts to one side and busied himself with plans for his people's prosperity. He pushed himself day and night, planning new wheat cultivations, some up to 40 miles from Rangihoua. He planned a European-style town, marking out the ground on a hill near Te Puna. He interrupted these activities at times to help the missionaries, building an enclosure so that a Christmas service could be celebrated on the shore. His position as senior chief at Rangihoua was by now assured, but he feared for his life; he told the European visitor John Liddiard Nicholas that the other chiefs, jealous of his wealth, would kill him. Careful to impress on fellow chiefs the numbers of his European weapons, he was accorded a healthy respect.
On 13 February 1815 Ruatara fell ill. Nicholas discovered him with a raging fever and symptoms of what appeared to be a heavy cold. By 19 February, when Marsden realised he was ill, his condition had deteriorated; he was experiencing pain, and death was imminent. His relatives made tapu the place where he lay, and Marsden had to threaten to rase Rangihoua to the ground with the Active's big guns before he could gain access to him. Marsden and the other missionaries gave him food and medicine, but without effect. On 2 March Ruatara was carried to a specially constructed shelter on the hill at Te Puna; the following day he died there. His wife, Rahu, hanged herself the next day. Seven chiefs, including Hongi Hika, assisted in laying out the body, and were tapu, unable to feed themselves, for varying periods. In April Ruatara's remains and those of his wife were carried inland to Motutara, his tribal lands.