Following the commencement in March 1860 of hostilities at Taranaki, in one of the main phases of the New Zealand Wars, Nixon submitted a proposal to the New Zealand Government for the raising of a force of colonial volunteers. He was made a lieutenant colonel in the Auckland Militia and formed the Royal Volunteer Cavalry, which had responsibility for the townships at Otahuhu, Panmure, and Howick. He also led his forces ensuring the security of the communication and supply routes from Auckland through to defensive positions in South Auckland. In 1861, he stood for the House of Representatives as the member for the Franklin electorate, which encompassed most of rural South Auckland, and was duly elected on 28 January.