This interdisciplinary study examines the International Criminal Court (ICC) as a legal institution functioning within international politics by analysing the influence of the international legal norms concerning individual criminal responsibility on the outcomes of ICC prosecutions. Much of the international relations literature focuses on the opening of investigations and the selection of suspects at the ICC. Specifically, the ICC’s poor record of successful prosecutions – consisting of only five convictions for core international crimes as of 2021 – is often explained by pointing out that international criminal justice proceedings generally follow the political interests of states and elites, thus, reproducing global structural inequalities by prosecuting actors without powerful political backing. However, the outcomes of ICC trials and the process of assessing the criminal responsibility of those individuals standing trials have remained significantly underexamined in the international relations literature. To address this gap, this thesis examines the outcomes of ICC trials with respect to what I call the ‘politics’ of the legal field, namely, the promotion and contestations of different understandings of the law by various actors. Based on an analysis of over 200 legal documents, 330 academic publications, NGO articles and state statements, this thesis argues that the idea that international trials should apply the laws on criminal responsibility in a narrow and predictable fashion, regardless of the trial outcome, gained significant support among ICC judges and many legal experts outside the Court. From the perspective of ICC judges, the restrained approach to criminal responsibility serves the purpose to institute a stable international legal order. Thus, by combining insights from international relations and legal studies, this thesis contributes to the literature on international criminal justice, by elucidating and examining in detail an important contributing factor to trial outcomes at the Court, namely, the ideological battles taking place within the field of international criminal law.