Pōmare, originally named Whētoi, the son of Puhi of Ngāti Manu, was born in the latter part of the eighteenth century. He was connected by descent to Ngāpuhi hapū Ngāti Rangi, Ngāti Rāhiri and Ngāti Hine, and to the independent tribe Ngāti Wai. In October 1814 Samuel Marsden, the chaplain of New South Wales, told Bay of Islands people of the conversion to Christianity of Pōmare of Tahiti; Whētoi at once adopted the name Pōmare as his own. His elder sister, Haki, was the mother of Whiria, later known as both Whētoi and Pōmare II.
Ngāti Manu were originally a people of Tautoro, south of Kaikohe, but quarrels with Ngāti Toki in Pōmare's lifetime drove them away; one group followed Pōmare's aunt Hautai in settling at Manurewa, near Taumārere. From there Pōmare and other chiefs led groups to establish pā and villages at Kororāreka (Russell), Matauwhi, Ōtūihu, Waikare and Te Kāretu. Pōmare was chief over Matauwhi, a cove a little south of Kororāreka in what is now called Pōmare Bay. His neighbours at Pāroa and Rāwhiti were Ngare Raumati, who had been at war with Ngāpuhi for two generations.
The increasing frequency of visits of European vessels willing to trade iron tools, and, later, muskets and powder for food supplies, wood, water and recreation, and the advent of the missionaries, also anxious to trade, created opportunities which Pōmare exploited single-mindedly. He traded for tools so that his people could produce surplus crops to exchange for weapons. Muskets acquired in this way afforded security against the northern Bay of Islands alliance led by Hongi Hika, Tāreha, Rewa (Mānu) and Ruatara.
The first missionaries with whom Pōmare came in contact were seeking timber, which he supplied with great efficiency. These visitors portrayed his character variously as artful, covetous, ambitious, boastful, dominating and independent, yet they showed he was also capable of compassion. Of all the Bay leaders he was the most useful to them. He was an excellent judge of the quality of European goods. He was also the acknowledged expert in the Bay in the difficult art of preserving human heads. Pōmare went to visit Port Jackson (Sydney) in the missionary vessel Active in July 1815. By 1819 the missionaries regarded him as one of the four most important men in the Bay of Islands, together with Hongi Hika, Te Whareumu and Rākau. He expressed an interest in Christianity, but it was probably for practical reasons that he kept on good terms with the missionaries and extended hospitality and protection to Thomas Kendall.
Pōmare's arming of his people allowed him to rival Hongi and other chiefs as a war leader. In the last seven years of his life war parties recruited and led by Pōmare brought devastation to many areas, resulting in depopulation and a tribal regrouping that was to have lasting effects on Maori society. Rumours of Pōmare's approach caused as much disruption as actual attacks: only Hongi was more feared.
During the winter of 1820 Pōmare led a war party to the East Coast. One of his attacks there involved the six month siege of Te Whetū-matarau pā at Te Kawakawa (Te Araroa), which was defended by a number of East Coast hapū. The highest-ranking person in the pā was Te Rangi-i-pāia, wife of Ngārangitokomauri, one of the leaders of the besieged pā. When food was so short that the defenders were reduced to cannibalism, Pōmare pretended to give up the siege, only to return as the defenders streamed out to find food. The pā was taken, many people killed and others captured. Te Rangi-i-pāia was taken back to the Bay of Islands as one of Pōmare's wives.
Pōmare joined Hongi Hika and other Bay leaders in the 1821 attacks on Mauinaina pā, at present day Panmure, Auckland. The combined Ngāpuhi contingents then moved to the attack on Te Tōtara pā, on the banks of Waiwhakauranga Stream, in the Thames area. Although he had used similar tactics at Te Whetū-matarau, Pōmare is said to have withdrawn from this campaign because he disapproved of the plan to take the pā by treachery. In 1822 Pōmare went to the Bay of Plenty, first attacking the people defending Ngāuhiapō pā on Tūhua (Mayor Island), and then pursuing Ngāti Awa, Ngāti Pūkeko and other peoples up the Whakatāne River valley and into Tūhoe country.
After a brief return home, Pōmare joined the 1823 massed Ngāpuhi attack against Mokoia Island, Rotorua. At Mokoia the underlying hostility between Pōmare and Hongi Hika became evident; the contingents of Pōmare and Te Wera Hauraki attacked the island before the arrival of Hongi's party, but were driven off and forced to fall back on Hongi for protection. Pōmare quarrelled with Hongi possibly because he was humiliated by this defeat. Pōmare wished to settle the matter by an appeal to arms on the spot; Hongi refused. After the capture of Mokoia, Pōmare and Te Wera Hauraki separated from the main body, leading their war party to the East Coast. After various skirmishes, Pōmare attempted to make peace with Te Rangi-i-pāia's people, but Ngāti Porou attacked him at Te Uma-o-te-aowetea. They were again defeated. Pōmare's peacemaking efforts were finally successful. Te Rangi-i-pāia was reunited with her people, but returned to the Bay of Islands with her husband.
In 1824 Pōmare set out again, fighting in the Kaipara district in March, probably against enemies of Ngāti Whātua. He then moved to Wairoa, north of Ahuriri (Napier), having been recruited by the Urewera chief Te Maitaranui to help him avenge deaths caused by Ngāti Kahungunu. Pōmare took the pā Titirangi, near Waikaremoana, and took part in a campaign of harassment of the people of the Wairoa district. Later in this year Pōmare may have assisted Te Whatanui and Ngāti Raukawa against the people of Heretaunga (Hawke's Bay). On Pōmare's return to the Bay of Islands he was accompanied by a party of Ngāti Kahungunu from Wairoa, who were encouraged by him to visit the north in the hope of obtaining guns. He established them on lands at Te Kāretu, while he lived in his house, Te Kata-o-te-kawariki, at the other end of the village.
Pōmare set out to war again in 1826, on the mission that was to result in his death. Accounts differ as to whether his campaign was directed against Ngāti Maru or Waikato, but all agree that he was killed about June 1826 by a combination of these people. Most accounts also agree that his small party was surrounded and destroyed at Te Rore, on the Waipā River. His body, as well as those of his party, which included his son, Tītaha, was eaten.
The death of Pōmare had many repercussions in the Bay of Islands. Attempts to avenge his killing had little effect: it was as if his death had undermined Ngāpuhi confidence in their invincibility. After his death he became known as Pōmarenui (Pōmare the Great), to distinguish him from his nephew, the heir to his mana, Pōmare II.
Pōmare had several wives and children. Waihanga of Te Kapotai hapū, whom Pōmare had executed for adultery, was the mother of Tiki, also known as Hirepo, Heikai and Heitiki; the killing of Tiki in March 1828 by Te Māhurehure people nearly provoked war between Ngāpuhi of Hokianga and the Bay of Islands. Another wife, Hoi, was the mother of Raukatauri. After Pōmare's death Te Rangi-i-pāia married Te Kariri and returned to live on the East Coast.