Arnold was a Victorian Radical. As government inspector of public works in the 1860s, he found work for unemployed Lancashire cotton workers. He became editor of the Liberal evening newspaper The Echo and was a great writer on social questions ranging over church disestablishment, land law reform, reform of metropolitan government, state ownership of the railways, public works during periods of distress, temperance reform, women’s political enfranchisement and reform of the married women’s property laws. He failed to get elected to Parliament at Huntingdon in 1873 but won Salford in 1880 and after losing turned to London politics becoming an Alderman and Chairman of the London County Council 1895-97.