He was selected for the Namibian squad to play in the 2007 Rugby World Cup where he made three appearances. Having appeared in the Africa Cup in 2008 and 2009 and the RWC 2011 Qualifiers he now[when?] has 23 full international caps. He was a member of the victorious Namibia Squad that won the 2010 IRB Nations Cup which went alongside their 2009 African Cup win.
He received the Man of the Match award in a 2011 Rugby World Cup match against Wales in which his Wasps team mate Heinz Koll scored a try. However Namibia lost the match 81-7.
He has played club rugby in Namibia for Wanderers RFC, and professionally in England for Rotherham Titans RFC. He was named Rotherham's player of the year in 2009. In December 2011 he joined London Wasps, on a deal taking him through to the end of the season. Having impressed during his time at Wasps Du Plessis was awarded a two year contract.