A leading figure on the South African stage, Ernie raced saloons and GTs, finishing third in an Alfa Giulietta GTI in the 1958 Rand 9 Hours, before eventually joining the burgeoning single-seater series in the early sixties.
Racing an Alfa-engined Heron Special in 1961, he scored his first single-seater victory at Kyalami and later that year won the Rhodesian GP at Belvedere.
He continued with this car into 1962, but soon replaced it with an ex-works Lotus 21-Climax 4, becoming national champion after a thrilling season-long battle with Syd van der Vyver. Joining the Lawson Organisation should have brought even more success in 1963 but, despite a whole clutch of top-three finishes through to the end of 1964, outright wins were to elude him.
Pieterse slipped from competition at this level after failing to qualify for the South African GP on New Year's Day 1965.