In 1880, he was elected as one of two members of parliament for Salford, with the Liberals gaining both seats at the expense of the Conservatives. The Redistribution of Seats Act 1885 split the parliamentary borough of Salford into three single-member divisions, and Arnold stood unsuccessfully for the new Salford North constituency in 1885 and 1886. At the 1892 general election he stood at Dorset North, but again failed to be elected.
