Sustainable Public Food Procurement (SPFP) is gaining recognition for its potential to improve the sustainability of food systems and promote healthier diets. However, SPFP faces various challenges, including coordination issues, actor dynamics, infrastructure limitations, unsustainable habits, and institutional resistance, among others. Drawing upon insights from the Multi-Level Perspective (MLP) on socio-technical transitions and the X-curve model on transition dynamics, this study investigates the role of transition intermediaries in facilitating SPFP-induced transformations in food systems. Focusing on four case studies in Spain, (...) we identify common barriers encountered in SPFP and analyse how distinct types of transition intermediaries contribute individually and collectively to address these challenges. Additionally, we explore how intermediary networks evolve throughout different phases of the transition process. Our findings reveal that SPFP barriers are systemic and interconnected, emphasizing the necessity of collective intermediation to overcome these obstacles. Furthermore, our results reveal how collective intermediation is orchestrated by pivotal intermediaries who mobilize diverse transition intermediaries, shaping multiple transition pathways. These intermediaries operate at both food system regimes and niches, challenging the conventional notion that transformative change can only originate from niche efforts. Lastly, we highlight the dynamic and flexible nature of intermediation in SPFP transitions, underscoring the importance of adaptability in strategies as these transitions evolve over time. Practical implications include the need for context-specific, adaptive approaches and strategies that leverage intermediary diversity. This research offers insights for policymakers, practitioners, and scholars into SPFP and broader transitions towards food systems transformation, fostering a more comprehensive understanding of these transition processes. (shrink)