Simpson was born on 8 January 1984 in Poole, Dorset, England and he moved to South Africa with his family when he was 10 months old. He studied at the South African College High School and matriculated in 2002.
Simpson began karting at the age of 8 and won several regional and national karting titles.
In 2000 Simpson became the youngest ever driver to win the South African Formula Ford Championship, at the age of 16. In 2001 Simpson left his native South Africa to compete in the Slick 50 Formula Ford Zetec Championship in Britain. Despite poor funding the youngster was highly impressive beating the 'works' teams on a number of occasions and culminating in being awarded the Motorsport News Race Ace award for his performance at Donington Park. He ended the season with a stirring performance in atrocious conditions at Brands Hatch in the Formula Ford Festival, an event previously won by Eddie Irvine and Johnny Herbert.
For 2002 Simpson was signed by Durango to compete in the European Formula Renault Championship and Italian Championship, however his season was dogged by bad luck and a serious lack of testing.
Just weeks before the 2003 season got underway, a potential sponsor pulled out, leaving Simpson high and dry, without a drive. Undaunted, the youngster concentrated on his fitness, and continued looking for the right drive.
For 2004, Simpson joined Richard Dean’s Team JLR, with which he contested the prestigious British Formula Renault Championship. He finished second in the Winter Series with two wins and five podiums to his name.
Simpson was brought into race in the inaugural A1 Grand Prix World Cup of Motorsport in winter 2005, helping A1 Team South Africa to 17th place in the series. His best result was a third place in the Feature Race in Dubai, and he also achieved a fifth at his home event. Simpson also continued to drive for Team JLR in British Formula Renault.
For 2006 he was signed to drive for Gelles Racing in the Champ Car Atlantic Series, he left the series after three races, with a best finish of 5th. Towards the end of the year he had a test with Champ Car World Series team Mi-Jack Conquest Racing and reportedly impressed the team with his performance.
In 2007 he signed with Kenn Hardley Racing to compete in the Indy Pro Series. He struggled with the oval races on the series, but finished well on the road and street courses, recording a season best 3rd place finish at the Mid-Ohio Sports Car Course and finished 9th in the championship. Kenn Hardley racing shut down at the end of the season and its assets were sold. Simpson was unable to find another team to continue in the series with in 2008.
After a challenging few years without any driving, Simpson was back in a full time race seat in 2014 driving for JDC Miller Motorsport in the Tudor United SportsCar Championship. A highlight of the season was a 3rd place finish at Road America. In 2015, Simpson raced in selected races in the Tudor United SportsCar Championship and finished 3rd at the Daytona 24 Hours, 2nd at Detroit and had a Pole Position at Lime Rock Park. During 2015, Simpson was also a race driver for LAP Motorsport, the official team of MINI USA.
Simpson won the PC class of the Daytona 24 hours in 2016, part of the WeatherTech SportsCar Championship.