Born in Dundee, Williamson began karting at the age of eight, and spent a successful decade racing in the various classes around the United Kingdom.

By the time Williamson moved into the junior formulae in 2008, he had claimed three Scottish karting championship titles at Cadet and MiniMax levels, before taking a clean sweep in 2008.

He also contested the Estoril round of the Portuguese Formula Renault 2.0 Winter Series, taking second and fifth-place finishes for CR Scuderia.

[2] CR Scuderia, under their new name of CRS Racing, signed Williamson for the 2009 season as part of a four-car team alongside Harry Tincknell, Matias Laine and Joshua Scott.

Williamson won both races from pole position, to trail Blomqvist by one point on dropped scores heading into the final round at Brands Hatch.