He later returned to the Renault Clio Cup United Kingdom in 2013.

Williamson began his career in the SAXMAX Saloon Car Championship in 2006.

He ended the season eleventh in the championship standings.

He stayed with FML for the 2011 Ginetta GT Supercup season, where he ended second in the G50 Cup class standings.

In September 2012, it was announced that Williamson would make his British Touring Car Championship debut with Team HARD.