Of Ngati Whanaunga descent, Mangakāhia was born in Waikaurau on the Coromandel Peninsula.

As a leading organiser of the movement, he was nominated by fellow chiefs Henare Tomoana and Te Keepa Te Rangihiwinui to the position of Premier, which he held for the duration of the 1892 sitting of the parliament.

Prior to his involvement in Te Kotahitanga, Mangakāhia unsuccessfully contested the Western Maori electorate in the New Zealand Parliament in the 1881 and 1884 elections.

In 1881, he came a distant second of four candidates, trailing Wiremu Te Wheoro by over 53% of the vote.

[4] He was married to Meri Te Tai Mangakāhia, a leading figure in the movement for Women's suffrage in New Zealand.