Van der Merwe began his motorsport career in the junior single-seater categories. His most prominent early achievement came in 2001, when he won the prestigious Formula Ford Festival, a result that announced him as one of Britain's emerging single-seater talents.
In 2003, van der Merwe claimed the British Formula 3 Championship title, one of the most competitive junior championships in the world and a traditional stepping stone toward Formula One. He followed that success by moving up to Formula 3000 in 2004, racing for Super Nova Racing. His campaign was cut short mid-season when his sponsorship funding was exhausted, forcing him out of the championship. He subsequently secured a contract as a part-time tester for the BAR–Honda Formula One team, gaining experience alongside a top-tier constructor without a race seat.
Van der Merwe represented A1 Team South Africa in the A1 Grand Prix series during the 2005 and 2006 seasons. The national-team format of A1 Grand Prix suited drivers looking to remain competitive outside the traditional Formula One pathway. His best finish in the series was seventh place, achieved in New Zealand.
In 2006, van der Merwe participated in the Bonneville 400 project, an initiative by BAR–Honda to set an official land speed record for a Formula One car. Driving a modified BAR–Honda 007 on the famous Bonneville Salt Flats in the United States, he accelerated the car to speeds in excess of 400 kilometres per hour, joining the Bonneville 200 MPH Club in the process. The attempt was aimed at establishing a formal FIA-sanctioned land speed record for a Formula One specification vehicle.
Van der Merwe also competed in endurance racing. In 2008, he drove for James Watt Automotive in the 1000 km of Silverstone, a round of the 2008 Le Mans Series, where he finished 33rd overall and completed 159 laps.
From 2009 until the end of the 2021 Formula One season, van der Merwe served as the official driver of the FIA medical car. The medical car follows the Formula One field at the start of each race and is deployed at the scene of any serious accident, carrying an FIA medical delegate to provide immediate on-track medical support. The role demands not only high-speed driving ability but also the capacity to operate under extreme pressure in emergency situations.
He had also returned to A1 Grand Prix competition in 2009 for the series' final round at Brands Hatch before fully committing to his FIA duties.
Van der Merwe's tenure as medical car driver spanned twelve seasons, making him one of the longest-serving occupants of that position. His time in the role ended after the 2021 season when the FIA replaced him following his decision not to receive a COVID-19 vaccination.
Van der Merwe's career illustrates a path relatively uncommon in top-level motorsport: a driver who achieved genuine junior single-seater success, including a British Formula 3 championship, but found a lasting and impactful role not through a race seat but through the safety infrastructure that underpins Formula One. His twelve years as medical car driver placed him at the heart of Formula One's emergency response system during a period when the sport continued to refine its safety protocols, and his presence at grands prix became a constant feature of the pre-race and incident procedures seen by audiences worldwide.