Nuku, said to have been called Nuku-pewapewa because his moko was in the style called pewapewa, was born probably in the late eighteenth century, in Wairarapa. He was descended from the ancestors Kahungunu, Rangitāne, Te Aomatarahi and Ira. His principal hapū was Ngāti Kahukura-awhitia. Some genealogies suggest that Nuku-tūmārōrō was his father. It is more likely that he was the son of Te Ono, Nuku-tūmārōrō's second son, and his wife, Parahako. Earlier biographies have attributed to him the warlike exploits of an ancestor, also called Nuku, who lived five generations before. Both men exhibited ingenuity and skill in war; this could have helped to cause the confusion.
Nuku-pewapewa was a prominent leader in the period of disturbance between 1820 and 1839, when wars and migrations caused upheaval among the peoples of both islands. About 1820 a war expedition from the north, led by Tūwhare, Patuone, Nene and others, reached Wairarapa. The war party possessed muskets, a new weapon to which the old name, pū, a traditional war trumpet, had been given. When Nuku-pewapewa learned that Tūwhare and his allies were coming armed with pū, he is said to have replied: 'Let them come, let them blow their pū; my men can also blow pū.' Many war trumpets were sounded as the enemy approached, but their pū were muskets and many of Nuku-pewapewa's people were shot.
The next day he set up an ambush and captured three muskets and some of the marauding party. He tried to get the prisoners to show him how to use the new weapons, but they tricked him by loading them incorrectly. When the muskets would not fire, the prisoners explained that they were tapu and would only fire when aimed to kill. Nuku-pewapewa then tried them out against Rangitāne of the Moawhango district, but they still would not work. He abandoned them, and won a victory using traditional weapons.
Tūwhare's expedition went to Te Whanganui-a-Tara (Wellington Harbour) and then to Porirua. There Nuku-pewapewa attacked them, and regained his mana by capturing Te Ata-o-te-rangi, Taunuha, Korewa and six others. This victory enhanced his reputation, and he was invited to Heretaunga (Hawke's Bay) by Te Pareihe, the war leader of Ngāti Te Whatuiāpiti, to help 'extinguish the fires' kindled at Te Roto-a-Tara by an invading force led by Mananui Te Heuheu Tūkino II of Ngāti Tūwharetoa.
At this time Te Pareihe wanted the Heretaunga people to withdraw to Nukutaurua, on the Māhia peninsula, because his tohunga, Ngoi, had predicted massive invasions of Hawke's Bay. But many refused to go. While the departure was being discussed by the people of Heretaunga, collected together in the pā Tāne-nui-a-rangi, Nuku-pewapewa and the Wairarapa refugees arrived at Waimārama. There they built the pā Te Pūtiki. The Heretaunga leaders Te Moananui and Te Hāpuku wished to attack them, but the Waimārama elder Tuaha rebuked his relatives: 'When will it be the time for compassion?'
Nuku-pewapewa withdrew with Te Pareihe to Nukutaurua. There they lived for some years, in partnership with Te Wera Hauraki and his Ngāpuhi people. They built up their supplies of muskets by trading with American whalers, and became involved in the East Coast wars of the 1820s. Nuku-pewapewa, with Te Pareihe, helped Te Kani-ā-Takirau of Ngāti Porou take vengeance against Te Whakatōhea and Ngai Tai for the killing of a Rongowhakaata man. In spite of receiving valuable gifts (including a fine war canoe) from Te Kani-ā-Takirau, Te Pareihe was doubtful about going to his aid. When asked for his opinion, Nuku-pewapewa replied in words which have become famous: 'Never turn back when the voice of war is sounding in your ears.'
Nuku-pewapewa accompanied Te Wera Hauraki and Te Pareihe in a major punitive raid against Mananui Te Heuheu. The expedition consisted of 1,600 warriors; it overthrew the pā at Ōmakukura, on the north-west side of Taupō, killing at least 400 people. Peace was arranged by Te Rohu, the daughter of Mananui. While Te Pareihe and Nuku-pewapewa were involved in war on the east coast, news arrived that Te Momo-a-Irawaru of Ngāti Te Koherā, a hapū of Ngāti Raukawa, had occupied Te Roto-a-Tara. Te Pareihe, Te Wera Hauraki and Nuku-pewapewa led a force which succeeded in taking Te Roto-a-Tara by storm. Te Momo was killed nearby at Kahotea, and his attempt to occupy southern Hawke's Bay thus failed. Later, news came to Nukutaurua that Te Whatanui of Ngāti Raukawa, with Rangitāne allies, had invaded Hawke's Bay through the Manawatū Gorge, killing several chiefs, in order to avenge the death of Te Momo-a-Irawaru. Nuku-pewapewa and Te Pareihe led a war party to punish Ngāti Raukawa and Rangitāne. A battle took place at Te Ruru, near present day Dannevirke; the eastern sections of Rangitāne were the main victims.
While Nuku-pewapewa was away from Wairarapa, the district was invaded again, this time by the Taranaki peoples Te Āti Awa, Ngāti Tama and Ngāti Mutunga. After the defeat of the Wairarapa people at Pēhikatea about 1833, the majority went north to Nukutaurua. Although the accounts which have been preserved are conflicting, it is most likely that Nuku-pewapewa heard of the fresh invasion from refugees arriving at Nukutaurua, and began to plan to expel the invaders.
Although he was warned not to go, Nuku-pewapewa led a Wairarapa force of 200 to Maungaraki, a range south-east of present day Masterton. He was accompanied by Te Hapūku, leading a force of 400 Heretaunga men. The leaders climbed a hill at night and saw the innumerable fires of their enemies. Except for a few, led by Hoeroa of Ngāti Te Ūpokoiri, the Heretaunga forces withdrew. In spite of this defection, Nuku-pewapewa took by surprise the pā at Tauwhare-rata (near present day Featherston), where Te Wharepōuri, the leader of Te Ati Awa, was living.
Te Uamairangi and Te Kakapi, the wife and the adoptive stepdaughter of Te Wharepōuri, were captured, with 25 others. Nuku-pewapewa spared the lives of the captives, and sent Te Uamairangi to her husband, in an effort to make peace. In response Te Uamairangi presented Te Kakapi to Nuku-pewapewa. This laid the basis for the peace that was later concluded. Nuku-pewapewa returned, with Te Kakapi, to the north.
After these battles Te Wharepōuri went north to negotiate the return of his niece and adopted daughter. The price was to be the restoration of Wairarapa to its dispossessed people. However, Nuku-pewapewa was not there to arrange the peace. He had been travelling south as Te Wharepōuri sailed north. At Tāhaenui, between Nūhaka and Whakakī, near Wairoa, his canoe overturned in the mouth of the river; a wave lifted the canoe above him and it struck him on the head, killing him.
Peace with Te Wharepōuri was made by Pehi Tu-te-pakihi-rangi, and beginning in 1841 the Wairarapa people returned to their homes. Through the efforts, valour and wisdom of Nuku-pewapewa the mana of the Wairarapa people was preserved. His canoe was carved and erected as a monument at Whakakī. A carved figure representing him was built into the palisade at the Pāpāwai marae near Greytown.