The United Nations War Crimes Commission (UNWCC), which operated between 1943 and 1948, is considered the most important multinational body set up by several Allied nations to investigate and consider war crimes committed by Axis powers during the Second World War. Remarkably, the Union of South Africa, one of the four prominent British dominions of the period, was initially involved in setting up the UNWCC but, in the end, did not become a full-time member. In this regard, South Africa is unique compared to the other dominions of Australia, New Zealand, and Canada, which all remained members of the UNWCC until its disbandment. Although the Soviet Union’s absence from the UNWCC has enjoyed some scholarly attention, South Africa’s absenteeism is yet to be examined. This article explores some of the reasons behind the Union’s initial cooperation and eventual withdrawal from the UNWCC. It is argued that the South African government utilised the term “war criminal” and “traitor” almost synonymously, simultaneously enabling the government to pursue several individuals possibly guilty of high treason, but also leading to the government overlooking other transgressions which aligned with the international law definitions of war crimes both by and against South Africans. It is illustrated that the South African political situation influenced how the government investigated and prosecuted individuals possibly guilty of wartime offences. To shed more light on this phenomenon, this article firstly explores the South African government’s stance towards and involvement with the UNWCC between 1943 and 1948, and secondly, discusses how the government prosecuted war criminals and traitors post-1945.