Kereopa was probably baptised by Father Euloge Regnier during the 1840s and may have served as a policeman in Auckland during the 1850s. He is known definitely to have fought for the King Movement during the Invasion of the Waikato in 1863. His wife and two daughters were killed in the massacre by government forces following the attack on Rangiaowhia near Te Awamutu, and his sister was killed in defence of the Hairini Line a few days later.
Shortly afterwards he met up with the prophet Te Ua Haumene and converted to the Pai Marire faith. In December 1864 he was sent on a mission to the tribes of the East Cape. His instructions were to go in peace and avoid confrontations with the Pakeha. However at Opotiki the missionary Carl Volkner, a suspected government spy, was seized, hanged and decapitated. Immediately afterwards Kereopa preached a sermon from Volkner's pulpit during which the missionaries eyes were plucked out of his head and eaten. It should be pointed out that although this is abhorrent to modern thinking it was not inappropriate in the context of Maori warfare and gave Kereopa great mana or standing.
Kereopa and his Pai Marire followers then abandoned the people of Opotiki to the revenge of the Pakeha and retreated to the Urewera Mountains to preach their faith to the Tuhoe people. Later he tried to return to the Waikato but was repulsed by a war party of Ngati Manawa and Ngati Rangitihi. Following the resulting battle Kereopa is said to have eaten the eyes of three of the slain enemy. He then retreated to the Ureweras again where he found refuge and where he remained in hiding for the next five years.
However in the early 1870s the Ureweras were invaded by the government forces searching for Te Kooti and the Tuhoe were effectively conquered and subdued. Reluctantly they were forced to yield up Kereopa to Ropata Waha Waha. He was tried and hanged for Volkner's murder, 5 January 1872.