Simpson began his career in National Hot Rod in 2005, before graduating to the National Hot Rod European Series in 2006. He also raced in the National Hot Rod World Series that year. He went on to win the European series two times in 2009 and 2011, as well as finishing runner-up in the World series in 2008 and 2009. In 2013 he switched to the Quaife Intermarque Championship, winning back-to-back titles in 2013 and 2014. In November 2015, it was announced that Simpson would make his British Touring Car Championship debut with Speedworks Motorsport driving a Honda Civic Type R.
