The African Union (AU) has emerged as a central regional institution in promoting peace, security, and conflict resolution across Africa. This paper critically examines the African Union's role in peacebuilding and conflict resolution in South Sudan following the country's independence in 2011. Drawing on secondary sources, policy reports, and scholarly literature, the study analyses the origins of the South Sudan conflict, the AU's mediation initiatives, collaboration with the Intergovernmental Authority on Development (IGAD), and major peace agreements, including the Agreement on the Resolution of the Conflict in South Sudan (ARCSS) and the Revitalized Agreement on the Resolution of the Conflict in South Sudan (R-ARCSS). The paper further evaluates the AU's peacekeeping missions, humanitarian interventions, institutional capacity-building programmes, and support for transitional justice mechanisms such as the proposed Hybrid Court for South Sudan. While the AU has played a significant role in facilitating dialogue, reducing violence, and promoting regional cooperation, its effectiveness has been constrained by inadequate financial resources, weak enforcement mechanisms, competing interests among member states, and external geopolitical influences. The findings suggest that although the AU has contributed meaningfully to preventing further escalation of conflict and sustaining political negotiations, durable peace in South Sudan requires stronger institutional coordination, enhanced implementation mechanisms, greater accountability, inclusive governance, and sustained commitment from regional and international stakeholders. The study concludes that strengthening the AU's conflict prevention and peacebuilding capacities remains essential for achieving long-term stability and sustainable peace in South Sudan and across the African continent.