However at the outbreak of the Hutt Valley Campaign in 1846 he was firmly on the side of Te Rangihaeata in resisting the encroachment of European settlers onto Maori land. Te Mamaku and warriors of his hapu were with Te Rangihaeata in the attack on Boulcott's Farm in May, 1846. Aftrwards he sent letters to other chiefs in the Wanganui area urging them to join in the conflict. Some of these were intercepted and forwarded to the government and may have precipitated George Grey's decision to arrest Te Rauparaha.
Returning to Wanganui in Septemeber 1846 Te Mamuku told the settlers, some 200 Europeans, that he had no quarrel with them and would protect them from attack by other Maori but he would not tolerate the presence of government troops. Naturally two months later the government decided to station troops at Wanganui.
There was some skirmishing, nothing serious until in April 1847 a Maori was executed for the murder of a settler family; Te Mamaku reckoned he should have been handed over to tribal justice. After this raids on the outlying farms intensified and then in May Te Mamku lead the war party that began a serious siege of the town. Neither side was particularly keen to attack the other until July when there was a sort of half hearted battle. casualties were about equal on both sides and honour was satisfied so the Wanganui Campaign was over. It was to be seventeen years before there ws any further fighting between Maori and Pakeha in the district.
In 1857 Te Mamaku was offered the Maori Kingship, he declined but he he did join the King Movement in their opposition to sale of Maori land. He did not get involved in the Battle of Moutoa island but was probably fighting alongside the Hau Hau forces at Ohoutahi, Second Taranaki War.
Despite this he was within a few years regarded as a man of peace and had the respect of the government. He opposed Te Kooti but was firm in his belief that the King Country was sacrosanct Maori territory even to the extent of executing one man who persisted in entering the area. In 1880 he joined Kepa te Rangihiwinui in trust to protect the Maori land of the upper Wanganui River from sale to the Pakeha.
However in his later years he appears to have accpeted many of the changes that Europeanization brought to his area.
He died June 1887 at Taumaranui.