The agri-food sector plays a strategic role in decarbonization due to both its significant environmental footprint and its potential to drive circular and bio-based transitions. This article presents a scoping narrative review of the scientific literature on agri-food waste and by-product valorization pathways as systemic tools for greenhouse gas mitigation and circular bioeconomy development within the European context. Food loss and food waste are analyzed across all stages of the supply chain production, processing, distribution and consumption highlighting their implications for resource efficiency and climate impact. The review integrates technological options including anaerobic digestion, composting, biochar, biomaterials, biorefineries and 3D food printing with enabling dimensions such as digital traceability systems and policy frameworks. Particular attention is devoted to the role of structural factors, including small and medium-sized enterprises and territorial ecosystems, in shaping implementation pathways. Overall, the literature suggests that valorization strategies can reduce the carbon footprint of agri-food systems, foster bio-based markets and strengthen territorial resilience, although environmental benefits depend on scale, governance and effective integration within circular economy frameworks.