Moorhouse was elected to represent Akaroa in the 1st New Zealand Parliament, and remained an MP until his death. In his parliamentary career, he represented the Akaroa, Heathcote (a notice of election was gazetted on 12 July 1862, and the member sworn in on 14 July), Westland, Westland Boroughs, Christchurch and Ashley (elected 1879) electorates. In the 1866 election, he had won both the Mount Herbert and Westland electorates, and chose to represent the latter. At the 21 December 1875 election, he stood in the City of Christchurch electorate for the 6th New Zealand Parliament. He was returned in third position in this three-member electorate; the other members returned in the election were Edward Richardson and Edward Cephas John Stevens.