Van der Merwe made his provincial debut for WP in 1977 while a student at Stellenbosch University. He was selected on the replacement bench for the Springboks in the first tests against the touring British Lions in 1980. Van der Merwe made his test debut in 1981 against New Zealand on 29 August 1981 at Athletic Park in Wellington. He played his last test match for the Springboks, eight years later, against the World XV at Newlands. Van der Merwe also played in six tour matches for the Springboks.