Williamson was born in Inverness and began his playing career with local Highland League club Clachnacuddin FC.
As a youngster he joined Glasgow Rangers in 1988 under manager Graeme Souness at that time, only to return to Inverness due to homesickness.
Williamson spent five seasons playing for County in the Third Division, eventually winning the league title and promotion in his final year.
A leg break ended his playing career, and he was awarded a testimonial by Ross County which saw Coventry City visit Victoria Park.
In January 2007, Williamson became manager of Third Division side Elgin City, taking over at Borough Briggs following the departure of Brian Irvine.