International law, as a set of rules governing the relations between states and international organizations, has generally been studied from the perspective of classical legal and political perspectives. However, examining and analyzing this field from a philosophical perspective, especially from the perspective of the existentialist school, is able to reveal new dimensions of its fundamental concepts such as responsibility, freedom, the crisis of meaning and identity. The philosophy of existentialism, which emphasizes individual freedom, moral responsibility, the authenticity of choice, the crisis of identity and the meaning of life, allows us to analyze traditional concepts of international law such as sovereignty, the international responsibility of states, human rights and the identity crises resulting from globalization in a new light. This article, using a descriptive-analytical method, examines and carefully evaluates the concepts and elements common between the philosophy of existentialism and international law, and while accurately describing the principles and concepts of both fields, analyzes the challenges and opportunities that arise from the intersection of these two perspectives. In this regard, the theoretical foundations of existentialism, including the philosophical views of thinkers such as Sartre, Camus, and Heidegger, are first referred to, and then these foundations are compared with key concepts in international law. The main goal of this article is to redefine key concepts such as sovereignty and state responsibility from a philosophical and ethical perspective, and to provide a deeper understanding of the responsibility of states for their international decisions and actions.