This article examines relevant norms concerning trials conducted by courts established by armed non-state actors (referred to as ‘rebels’) during non-international armed conflicts. While such courts are often justified by rebels in the interest of securing law and order, states’ perceptions are more negative, especially the territorial state concerned. This raises questions under international humanitarian law, human rights law and international criminal law on the legality of such courts and of fair trial guarantees. Legal deficiencies may result in individual criminal responsibility for the individuals involved, including judges and those carrying out sentences. This article pays attention to the intention held by states when drafting relevant norms and a recent case where a domestic court in Sweden ruled on the individual criminal responsibility of a soldier for carrying out sentences issued by a rebel court, a first for any court worldwide.