As a young man, Harris was greatly impressed by the charismatic nonconformist minister, George Dawson, who preached the doctrine of social improvement and enlightened municipal reform subsequently known as the "Civic Gospel". He became a founder-member of Dawson's non-denominational chapel, the Church of the Saviour, in 1847, where fellow-members included George Dixon, J. T. Bunce, J. A. Langford, Robert Martineau, Samuel Timmins, A. Follett Osler, and Joseph Chamberlain. With many of these same individuals, he honed his political and reformist ideas at meetings of the Birmingham and Edgbaston Debating Society, of which he served as President in 1864–5. He spoke publicly in support of Lajos Kossuth and the nationalist cause in Hungary, Garibaldi's republican struggle in Italy, and the liberation movement in Poland; and in criticism of the British government's conduct of the Crimean War.