Between 1945 and 1949, the British military conducted a large number of war crimes trials in Europe and Asia. Based on historical archival records, among other sources, this article evaluates and compares the British authorities’ implementation of the 1945 Royal Warrant and war crimes trials in Europe and Asia, with a specific focus on trials organized in Germany and Singapore. By examining the British war crimes trial experience in those two jurisdictions, the article analyzes factors shaping the evolution of the Royal Warrant's legal framework and trial model in different contexts. It therefore contributes to the growing historical work on post-Second World War trials and current debates among scholars of transitional justice and international criminal law on the contextual factors that impact on war crimes trials.