International environmental law has evolved from a marginal position to one of the pillars of international public order. The International Court of Justice, as the main judicial organ of the United Nations, has played a decisive role in this process. Despite the increasing importance of the Court's decisions in the field of environment, no research has been presented so far that has systematically followed the evolution of the procedure of this authority from its beginnings to the most recent developments. The present article, using a descriptive-analytical method and by examining the Court's appeals and advisory opinions, answers the main question of how the Court's judicial procedure has led to the development of environmental obligations of states. The research hypothesis is based on the principle that the Court, by adopting an evolutionary approach and a broad interpretation of general principles, has moved from implicitly proposing principles in unrelated cases to explicitly identifying customary rules and ultimately norm-setting in the field of climate change. The findings show that the rule of no significant harm, sustainable development, and environmental impact assessment have evolved from implicit concepts to binding customary rules in different periods of the Court’s practice, respectively. The recent request by the General Assembly for an advisory opinion on climate obligations also confirms the Court’s capacity to rule in new transnational issues. Despite these achievements, structural limitations, including the system based on the consent of States, continue to be considered obstacles to the Court’s full effectiveness in this area.