Ngāpora was born early in the nineteenth century. He belonged to Ngāti Mahuta of Waikato. His parents were Hore and Kahurimu. He was the nephew of Te Rauangaanga and a cousin of Pōtatau Te Wherowhero. He was said to have fought as a young man at the defence of Mātakitaki pā against Ngāpuhi in 1822. He may have taken part in the wars fought in the 1820s and 1830s by Waikato against Taranaki tribes and Te Arawa of Rotorua. He and his family became Christians, and he took the name Tāmati (Thomas). His wife was named Hera. They had at least one daughter, also named Hera.
In 1848 Ngāpora wrote to Governor George Grey to express his concern about the decreasing power of chiefly authority in Māori society and its consequences for law and order. His letter was passed on to Earl Grey, the secretary of state for the colonies, whose solution to the problem was to suggest that chiefly authority be upheld by granting chiefs land titles and local jurisdiction. This suggestion was not taken up by the governor, however.
Ngāpora and many Ngāti Mahuta, including Te Wherowhero, left Waikato and went to live at Māngere. They agreed in 1849 to provide military assistance to protect Auckland. Ngāpora was an Anglican lay preacher, and also an assessor, or assistant to the resident magistrate in the affairs of the local Māori community. He was a strong supporter of temperance. He also built a stone church at his village of Ihumātao, near Māngere.
In the 1850s, when the King movement rose to prominence as an attempt to consolidate Māori authority and halt land sales, Ngāpora's inclination was initially against an intertribal Māori kingship. However, when Te Wherowhero was installed as King and returned to live in Waikato, Ngāpora remained at Māngere to act as the King movement's representative to the governor. In 1861, when Sir George Grey returned to New Zealand as governor, Ngāpora arranged for leaders of the King movement to meet him. At the meeting Rewi Maniapoto insisted on recognition of the Māori King's independence, which Grey would not grant. In 1863 the dispute over sovereignty moved towards war. Ngāpora warned the governor that war parties were gathering to attack the government outpost of Te Ia (Havelock, near Mercer), and that there were plans for a surprise attack on Auckland. In July 1863 Māori north of the Mangatawhiri River were required to give an oath of allegiance to Queen Victoria, or leave for Waikato. Ngāpora considered this requirement to be insulting, and refused the oath. Soldiers looted Māori property and an atmosphere of open hostility developed. Disillusioned, Ngāpora returned to Waikato. Meanwhile, on 12 July, Lieutenant General Duncan Cameron and British troops had crossed the Mangatawhiri River to invade Waikato. Although he did not take part in the fighting in Waikato, after the war and the confiscation of Waikato land Ngāpora went into exile in the King Country with Te Wherowhero's son, Tāwhiao.
Ngāpora lived at Tokangamutu (Te Kūiti) in the territory of Ngāti Maniapoto, and changed his name to Manuhiri (guest), to reflect his exile. Te Wherowhero had proposed that Ngāpora should succeed him but others, including Wiremu Tāmihana Tarapīpipi, had preferred Tāwhiao. Ngāpora became Tāwhiao's closest adviser, and his daughter, Hera, became the King's wife. His close connections with the King gave Ngāpora great influence within the King movement. He became, for a time, a follower of Pai Mārire. However, he tried to stop the war party of Ngāti Maniapoto which destroyed the government blockhouse of Pukearuhe (White Cliffs) in North Taranaki in February 1869, and was against the King movement's forces' joining Te Kooti in renewed war with the government.
The boundaries of the King Country were still closed to Europeans in 1879, preventing the construction of the railway line south from Hamilton. Rewi Maniapoto wanted to use the government's need for access as a means to negotiate the return of some Waikato land, but Ngāpora and other Waikato counsellors to the King opposed any peace settlement without the return of all confiscated lands. They saw Grey, now premier, as the author of their misfortunes. At a meeting at Hikurangi, near Kāwhia, in 1878, Grey offered the King movement 500 acres at Ngāruawāhia and the return of all unsold confiscated land west of the Waikato River. This was rejected as inadequate by Ngāpora and other Waikato leaders. At a meeting with Grey at Te Kōpua the following year, Ngāpora flourished a copy of Grey's proclamation of 1863 expelling Māori from South Auckland, and demanded the return of all confiscated land.
In 1881 Tāwhiao formally submitted to the government at Alexandra (Pirongia). He was accompanied by over 500 warriors, and by Ngāpora and other leaders. Ngāpora continued to live at Whatiwhatihoe, the royal village in the King Country, where he died on 5 August 1885. He was believed to be about 80 years of age. Rewi stayed with him during his last days and Tāwhiao came to see him before he died.