Indigenous Knowledge Systems (IKS) in Nigeria are integral to traditional legal practices, reflecting a unique synthesis of oral traditions and contemporary legal systems. The research utilizes qualitative interviews with judges and legal practitioners, complemented by quantitative data from court records to assess the impact of IKS on judicial decisions. Interviews revealed that IKS are used in up to 40% of legal arguments, particularly in cases involving customary laws. Quantitative analysis showed a correlation between the use of IKS and more lenient sentencing outcomes. The mixed methods approach has successfully highlighted the pervasive role of IKS in Nigerian law practice and its nuanced impact on judicial decisions. Further empirical research should include longitudinal studies to track changes over time, while policymakers could consider integrating IKS into legal education curricula for a more holistic understanding.