John Williams was born in Buckley. A prolific scorer in junior football, he played for Bury, though not in the Football League, and for Accrington Stanley before impressing on trial with Second Division club Birmingham. Williams signed for them in August 1908, and made his debut on 7 September 1908, playing at inside left in a 3-1 win at home to Bradford. He was given a decent run of games in the starting eleven, but failed to impress, and returned to Accrington Stanley in February 1909.

In the 1909 close season, he moved to Crystal Palace of the Southern League. With Palace his best position was centre forward or inside right, though he was capable of playing in any forward role. Described as "an eager, neat and busy little footballer who possessed a snappy tackle and plenty of enthusiasm and determination", he scored 58 goals from 149 appearances in all competitions, including scoring five in one match against Southend United in September1909. Williams remained with the club for nearly five seasons, during which time he won two caps for Wales. In February 1914 he joined Millwall, also playing in the Southern League, and remained with the club for about a year.

Williams made his international debut for Wales in the 1912 British Home Championship against Scotland at Tynecastle on 2 March 1912. Wales lost 1-0. His second cap came in a 3-2 defeat at Ninian Park against Ireland in the same competition.

Williams was married to Sarah. He enlisted in the 17th Battalion, Middlesex Regiment - the footballers battalion, and served in Northern France during the first world war. Reported missing, presumed dead on the 5th of June 1916, he is commemorated on the Arras Memorial and at Millwall F.Cs ground.