 Van der Merwe won the South African Rally Drivers Championship a record eleven times in 1975, from 1977 to 1985 and in 1988.Van der Merwe's IMSA career included time at Hendrick Motorsports during the Corvette GTP era, which also led to one NASCAR Sprint Cup for the team, Watkins Glen in 1990 when Hendrick driver Darrell Waltrip was recuperating from a severe leg injury at the Firecracker 400 final practice, where he finished 24th; van der Merwe had attempted to qualify for the 1988 Daytona 500 in a Hendrick-owned car, but failed to make the race.He also held the SA Saloon Car Championship (1994), SA Modified Saloon Car Championship (1994 & 2001), and won the 1996 Castrol International Rally ending in Swaziland.