While he was young, Williamson played
centre-forward for Coatham Grammar School. He also played at amateur level for Redcar Juniors and Redcar Crusaders before he kept goal for
Middlesbrough in a friendly game versus Cliftonville as a 17-year-old. Middlesbrough were very interested in signing him as a professional, but he only agreed under the condition that they allowed him to continue his interest in becoming a qualified
draughtsman. Williamson's first competitive appearance for the club was in a game versus Crook Town in the
Northern Football Alliance on 1 January 1902, with his league debut coming in a home game against
Bristol City on 19 April of the same year. Initially an understudy for
Scottish international Rab Macfarlane, he gained a regular place in
1903–04 and never looked back. Williamson's Middlesbrough service saw him make 602 appearances in all competitions, of which 130 were consecutive. His appearance total is still a
Middlesbrough record. He was nicknamed "Tiny", due to him being barely tall. He played in the last game at
Linthorpe Road and the first league game at
Ayresome Park. He scored two goals, both from the
penalty spot, though after he missed one against
West Ham United he never took another, after feeling the risk of racing back to his own goal was both too risky and tiring. He was Middlesbrough's first capped goalkeeper, gaining seven full
England caps. His first came against
Ireland in February 1905 in the first international to be played at Ayresome Park, in which he scored an
own goal. His next appearance did not come for six more years, with the brilliance of
Sam Hardy keeping him out of the team. Williamson's reserved occupation meant that he was exempt from a
call-up for
World War I.
The Football League refused to sanction his
benefit later, on the grounds that those years during the war did not count towards his Middlesbrough service. He did eventually receive a game however, versus
Chelsea. His final game came on 24 March 1923, a 1–0 defeat to
Cardiff City. At 38 years and 9 months old, he would be the oldest player to represent Boro until
Bryan Robson broke that record 74 years later. ==Retirement==