Customary law has long served as a mechanism for solving environmental conflicts, especially in communities where indigenous governance plays a central role in land and resource management. However, its recognition and integration with statutory legal frameworks vary across jurisdictions, shaping both its applicability and effectiveness. This study employs a mixed-method framework that combines doctrinal legal analysis, case law review (145 cases), document analysis (250 texts), and structured interviews (100 participants) with statistical modeling and forecasting techniques. Comparative analysis across multiple jurisdictions evaluates the interaction of customary and statutory legal systems, while mathematical models, including regression analysis, success indices, and conflict reduction probability functions, quantify the influence of customary law on dispute resolution and governance effectiveness. Findings reveal that jurisdictions with stronger integration of customary law resolve 78% of disputes successfully and experience a 33% reduction in land and resource conflicts over a ten-year period. Regression results further show that legal recognition of customary law significantly improves governance indicators, while institutional resistance remains a barrier to broader integration. Inevitably, customary law is a powerful but underused tool in the environmental toolbox. Enhancing legal pluralism, enforcement mechanisms, and policy integration could strengthen its role as a tool of sustainable environmental conflict resolution.