Although primarily a ruckman, Williamson also spent a lot of time in defense. He started out at Northcote where he was a member of a premiership team and kicked 18 goals in his debut season at St Kilda. Perhaps his best year was 1939 when he finished the Brownlow Medal count as his club's top vote getter. Williamson coached Brighton to their first and only VFA premiership in 1948. St Kilda signed him on as their coach for the 1952 season and he remained in the role for two years.