The entry of the Union of South Africa into the First World War, as well as the subsequent invasion of German South West Africa (GSWA), served as a trigger to the 1914 Afrikaner Rebellion. In September 1914, the Union Defence Force (UDF) suffered a major reverse at the Battle of Sandfontein. However, in addition to the German threat, South Africa faced a second, more serious internal threat. The socio-economic realities of early-twentieth-century South Africa, felt most keenly among rural Afrikaners, magnified the rift between the competing interests of Afrikaner nationalists and the Union Government loyal to the British Crown. The Union’s entry into the war was a step too far for many Nationalist Afrikaners and ultimately precipitated the outbreak of the Afrikaner Rebellion. While the rank and file of the Afrikaner rebels comprised a broad swathe of men, coming from diverse backgrounds, and with assorted reasons for rebelling, the rebel leaders included notable, influential men such as the former Boer generals Christiaan Beyers, Christiaan De Wet, Manie Maritz and Jan Kemp, among others. The rebel ranks also included defence force officers, such as Captain Josef Johannes (Jopie) Fourie, who famously failed to resign his commission in the UDF before taking up arms against the Union Government. Fourie was subsequently captured at Nooitgedacht in the district of Rustenburg on 16 December 1914, and after a hasty, publicly held, field court martial, he was sentenced to death and executed by firing squad a mere four days later – officially making him the only rebel to be executed during the Afrikaner Rebellion. This article investigates the capture, field court martial, and execution of Jopie Fourie during the Afrikaner Rebellion, and argues that it was indeed the first real test of South African military law since the establishment of the defence force in 1912.