Technological advancements have profoundly reshaped communication, business operations, and global supply chains. One of the most critical trans-formations in recent years has been the shift from traditional supply chain management to Sustainable Supply Chain (SSC), where environmental, social, and economic factors play a crucial role in decision-making processes. Sustainable supply chains integrate digital innovations, green logistics, and ethical sourcing to enhance operational efficiency while minimizing ecological impact. Supplier selection in a SSC plays a critical role in achieving sustainability goals. Choosing the right suppliers helps to reduce carbon foot-print, adopt ethical production processes and increase resource efficiency. In addition, working with suppliers that adopt sustainable practices strengthens brand reputation and minimizes operational risks in the long term. Given the complex and multi-criteria nature of supplier selection in SSC, this study proposes a novel Interval Valued Intuitionistic Fuzzy (IVIF) group decision-making approach to improve decision accuracy under uncertainty. The proposed framework integrates IVIF Analytic Hierarchy Process (AHP) to determine the importance of criteria and IVIF Additive Ratio Assessment (ARAS) to evaluate supplier alternatives. A real-world case study from Turkey is conducted to demonstrate the feasibility and effectiveness of the proposed model, offering valuable insights into sustainable supplier selection strategies.