Du Preez was part of the South Africa Under-20s team that played at the 2011 IRB Junior World Championship. However, on 13 November 2016 he was called into the Scotland squad for the Autumn International Series as an injury replacement, having qualified for Scotland through the three year residency requirement, although he didn't take part in any match. He was called up again for the 2017 Six Nations Championship, and made his debut against England at Twickenham before gaining his second test cap the following week in the final day victory over Italy. Du Preez made his first international start in November 2017, wearing the Number 8 shirt in a narrow 17-22 defeat to the All Blacks.