<p>Achieving sustainable livestock production requires farming models capable of reconciling environmental performance, economic viability, and social outcomes, particularly in less-favoured rural areas characterised by agro-climatic constraints. This study examines whether organic mixed crop-livestock systems can deliver integrated sustainability outcomes through diversified crop rotations incorporating legumes. Using a Living Lab approach implemented in a semi-arid Mediterranean region of Italy (Sicily), the study addresses three research questions: (i) to what extent legume-based rotations in existing organic mixed crop–livestock systems can ensure adequate production performance while maintaining environmental sustainability, particularly in relation to soil and natural resource conservation; (ii) whether the crop rotations adopted by organic livestock farms comply with the requirements of the European Union’s 2023–2027 Common Agricultural Policy (CAP), particularly eco-schemes supporting crop diversification; and (iii) whether livestock systems in less-favoured areas can serve as transferable reference models for other EU regions under comparable conditions. Sustainability performance was assessed using the FAO Sustainability Assessment of Food and Agriculture Systems (SAFA) framework, contextualised through stakeholder engagement and complemented by a quantitative farm-level economic analysis. Results indicate that legume-based rotations enhance environmental integrity, economic resilience, and social well-being, while governance dimensions show greater scope for improvement. Overall, organic mixed crop–livestock systems adopting legume-based rotations emerge as context-specific farming systems that can inform agroecological transition processes and CAP objectives in semi-arid Mediterranean areas.</p>