Hamiora Mangakahia, of Ngati Whanaunga, was born in 1838 on the eastern Coromandel Peninsula. Like many of his contemporaries he was raised as a Christian, but was also trained in the genealogy and traditions of his tribe. For the rest of his life he struggled to retain his family lands, rich in kauri and other timber. He was generally unsuccessful, and developed a lasting distrust of Europeans. But he did become an expert in Native Land Court procedure, and was invited to conduct cases from far afield. Nevertheless he was not a supporter of the Court, which he saw as a destroyer of Maori land and rangatiratanga (authority/chieftainship).
In 1891 he told the Native Land Laws Commission (the Rees-Carroll Commission) that the Court should be abolished.
Mangakahia's major achievement was his contribution to the Kotahitanga movement. This pushed for the abolition of the Native Land Court and all Maori land legislation. These would be replaced by Maori committees which would settle disputes according to Maori traditional law.
The movement also sought a degree of local self-government through a Maori (Kotahitanga) Parliament. According to Mangakahia this Parliament did not challenge the British Queen, but might allow Maori to control their lands and manage their own affairs. In his view such independence was protected and guaranteed by the Treaty of Waitangi, and by the unused section 71 of the Constitution Act 1852. This allowed Maori customary law to be used in predominantly Maori districts.
In 1892 Mangakahia was elected Premier of the Kotahitanga Parliament. His first step was to ask for a petition to be sent to the colonial Parliament. This called for the abolition of all laws relating to Maori land, and for Maori to control their own affairs. He continued to take an active role in the Kotahitanga Parliament and land issues until his death in 1918.
Hamiora's third wife was the suffragist Meri Te Tai Mangakahia.