Pōmare, often known as Pōmare Ngātata, was born in the early nineteenth century; his age was estimated as 30 in 1834. The names of his parents are unknown. He may have been descended from the chief Piritaka of Ngāti Kura hapū of Ngāti Mutunga. He was closely related to Ngātata-i-te-rangi of Ngāti Te Whiti and Ngāti Tāwhirikura hapū of Te Ati Awa. His wife was Tawhiti, niece of Te Rauparaha of Ngāti Toa; they had three children. The ancestral lands of Ngāti Mutunga extended from about 14 miles north of Waitara, Taranaki, to Mōkau, contiguous with those of Ngāti Tama.
While Pōmare was still a youth his people became involved in wars between the migrating Ngāti Toa and the Waikato tribes. In successive migrations after the defeat of Waikato at Motunui about 1822, sections of Ngāti Mutunga and Ngāti Tama joined the exodus of Taranaki peoples to the Kapiti Coast. Pōmare, with Ngātata, Te Poki and others, joined the migration to Waikanae about 1824 (Te Heke Niho-puta). Ngāti Mutunga moved to Te Whanganui-a-Tara (Wellington Harbour) after a year. Pōmare settled under Ngātata at Kumutoto Stream, erected a pā, felled the bush and established cultivations. The Wellington area was at that time occupied by Ngāti Ira, and Pōmare undoubtedly assisted Te Poki and Patukawenga, the senior Ngāti Mutunga chiefs, in their successful campaign to drive them out.
In revenge for their defeat at Motunui, Waikato took Pukerangiora pā, near Waitara, in 1831. After this disaster many more Taranaki people migrated south; tensions between them and Ngāti Raukawa culminated in the battle of Haowhenua in 1834, in which Pōmare's brother Te Waka-tīwai was killed. Tawhiti's brothers desecrated the grave in order to obtain some negro-head tobacco buried with the body. Pōmare, enraged at this violation of tapu, sent away his wife and the two youngest children. About this time he took Hera Waitaoro, daughter of Te Manu-tohe-roa of Puketapu, as a second wife. Te Rangitopeora, sister of Te Rangihaeata of Ngāti Toa, attempted to heal the breach between Pōmare and Tawhiti, even offering her own daughter Rākapa Kahoki and another young woman as additional wives, but Pōmare rejected them all.
The leaders of Ngāti Mutunga, and Ngāti Tama, recently returned from defeat in Wairarapa, now decided to leave the mainland for the Chatham Islands. Some of the Māori who had accompanied one H. Parker there in 1833 reported on the peace and plenty of the Chathams, and the defenceless state of its people. When the brig Lord Rodney arrived at Port Nicholson (Wellington) on 26 October 1835 amicable trading commenced, but four days later the crew were seized, and the master, Captain Harewood, was told by the chiefs that they wished to be taken to the Chathams, as they feared attack by hostile tribes if they remained. Over the next few days the ship was loaded with an estimated 70 tons of seed potatoes, and watered. The crew were permitted to slaughter and salt down 20 hogs presented to the master.
While these preparations progressed, the tribal leaders held a meeting on Matiu (Somes Island), and formal cession of their land at Waiwhetū and at Pito-one (Petone) was made to Matangi of Ngāti Te Whiti; Hēmi Pārai of Ngāti Haumia claimed the cultivations south of Ngāūranga and Te Aro had been ceded to his people by Ngātata and Pōmare. On 14 November 1835 the Lord Rodney sailed with 600 passengers; 100 of these disembarked at the heads, taking the second mate as a hostage. The ship arrived at the Chathams three days later, unloaded its passengers and cargo, then returned to Port Nicholson. Several chiefs sailed on the brig, and a second contingent of migrants embarked on 30 November. The second mate was released, and the master paid with quantities of potatoes, hogs, muskets and other weapons, and powder.
The various leaders had agreed that the land was not to be divided until their return, but Ngāti Tama immediately took possession of the Waitangi area. Ngāti Mutunga, Kēkerewai (a section of Ngāti Mutunga) and Ngāti Haumia then each seized a portion of the remainder, and enslaved the resident Moriori. The second contingent of migrants had no rights to land. They were granted occupation under the mana of the first comers. No consideration was given to the rights of the Moriori; those at Waitangi were nearly wiped out, although from a total Chatham Islands population in 1835 of around 2,000, only 160–200 were killed by the Māori immigrants.
Pōmare, who succeeded Patukawenga as senior Ngāti Mutunga chief about 1836–37, came to resent Ngāti Tama's occupation of Waitangi. His own people were cut off from trading with the whalers, and from some important seafood resources. Discontent was rife among the immigrants, and most began to plan to move again, to Norfolk Island or Samoa. Pōmare and Ngāti Mutunga were wrongly blamed for the taking of the French whaling ship Jean Bart, and their village and canoes were bombarded by the French warship Cécille. The loss of the Jean Bart had resulted from French panic rather than Māori aggression, but trouble arose because Ngātuna, chief of Waitangi, had insisted that the Jean Bart should trade with his people rather than with those of Pōmare. Ngāti Tama lost many of their leaders, killed by the French, and Pōmare took advantage of their weakness to drive them out of Waitangi. Many Ngāti Tama later returned to the mainland.
In 1840 Pōmare sold the Waitangi lands to R. D. Hanson, and in 1842 returned to Port Nicholson. On this visit he was baptised by Octavius Hadfield and took the name Wiremu (Wi) Piti (William Pitt). Pōmare later returned to the Chatham Islands, where he died on 29 January 1851. He was buried in the Wesleyan churchyard at Waitangi. His nephew, Wiremu Naera Pōmare, succeeded him as tribal leader.