Born in Florence, Williamson, who was ‘a well-known figure on Wearside’, was the eldest son of Sir Hedworth Williamson, who sat as a Liberal for County Durham, 1831-32, Durham North, 1832-37, and Sunderland, 1847-52.
In June 1864 Williamson came forward for a vacancy at Durham North, following the death of the sitting member, Lord Adolphus Vane. An advocate of non-intervention in American and Danish affairs, he championed Palmerston’s foreign policy, and was returned unopposed.
Williamson rarely spoke in the Commons, and his handful of known contributions chiefly concerned electoral reform. He supported the government’s proposal to enfranchise Durham University by uniting it with the University of London, 17 June 1867, and successfully led the opposition to altering the boundaries of South Shields and Gateshead, 11 June 1868, a subject on which he had given evidence to the 1867-68 select committee on the boundaries of boroughs.
At the 1868 general election Williamson headed the poll and thereafter backed Gladstone’s administration on most major issues, but was implacably opposed to Irish home rule.
