Abercanaid, Merthyr Tydfil born winger Rees Williams joined junior club Pentrebach in 1919 from where he was signed by new Football League entrants Merthyr Tydfil for whom he made his debut in their inaugural Football League fixture against Crystal Palace in August 1920. His performances at Merthyr brought him to the attention of Second Division Sheffield Wednesday who signed him in the summer of 1922 after 6 goals in 71 appearances for his hometown club.
At Wednesday he missed only one game as they won promotion back to the First Division as Second Division Champions in 1925-26, and by the time he joined Manchester United in October 1927 he had scored 8 times in 173 appearances for the Hillsborough club. His spell at Old Trafford was not particularly noteworthy, producing 2 goals in 35 appearances, before he joined non league Thames Association in 1929. He moved to Aldershot in 1930 before returning to Merthyr Town in 1931, and finished his career with a spell in Irish League football with Glenavon in 1932.
Williams also made eight appearances for Wales winning his first cap in February 1921 against Scotland and his last in November 1928 against England, scoring twice during his international career, both goals coming in a 2-2 draw with Ireland at Ninian Park in April 1927.