[2][3] Du Plessis was the third-highest scorer in the 2013 Under-19 Provincial Championship Division A competition for the Sharks U19,[4] scoring 116 points in eleven starts.
In April 2014, Du Plessis was named in the South Africa Under-20 squad for the 2014 IRB Junior World Championship.
He came on as a substitute in their 40–3 victory over Kenyan side Simba XV at City Park Stadium, Athlone.
[6] His first start came in the following match, a 27–11 defeat to the Eastern Province Kings in Durban, with Du Plessis scoring two penalties.
His cousin Daniël du Plessis is also a rugby player that represented the South Africa Under-20 team in 2015.