Digital platforms are increasingly central to circular economy transitions, yet it remains unclear how platform design translates into measurable circular outcomes. This study addresses this gap by developing a socio-technical framework that explains how digital platform information transparency and interoperability enable circular value creation. Drawing on socio-technical systems theory, platform governance, and the dynamic capabilities perspective, the study conceptualizes platform design features as layered affordances that operate through governance and knowledge-based mechanisms. Using survey data from platform-enabled supply chain actors and analysing the model via PLS-SEM, the findings reveal that transparency and interoperability significantly enhance sustainability governance mechanisms, while transparency strengthens knowledge sharing intensity and interoperability supports collaborative decision-making. Sustainability governance mechanisms, in turn, drive both circular business model implementation and circular supply chain performance, whereas knowledge sharing intensity primarily supports business model transformation. Notably, collaborative decision-making does not directly improve circular supply chain performance, suggesting that collaboration without governance alignment remains insufficient. By unpacking the indirect pathways through which platform design shapes circular outcomes, the study advances platform governance and circular supply chain literature. It offers actionable insights for managers and policymakers seeking to design digital ecosystems that move beyond symbolic digitalization toward measurable circular performance and systemic value creation.