This study examines how Irish primary school principals engage with curriculum development, mediation and enactment, particularly through their interactions with meso-level actors and activities. It builds on international research that highlights the growing complexity of curriculum reform and the pivotal role of school leaders in shaping its success. Situated within ongoing national curriculum reform, it examines how principals conceptualise curriculum, lead change and navigate a policy environment marked by complexity, fragmentation and reform intensity. It addresses a significant gap in the Irish educational research landscape, where the role of principals in curriculum leadership and the meso space remains underexplored. Guided by a social constructivist ontology and interpretivist epistemology, the research adopts a qualitative design. Data were generated through focus groups with practising primary principals and analysed using reflexive thematic analysis. Priestley et al.’s (2021) heuristic model of curriculum making and Bandura’s (1997) theory of self-efficacy frame the study, enabling a nuanced understanding of how curriculum leadership is experienced, interpreted and enacted at the school level and across system layers. Findings reveal that principals occupy a pivotal but often under-supported position as mediators of curriculum change. Their leadership is shaped by personal conceptualisations of curriculum, system coherence, emotional and relational dynamics and access to professional networks. Despite strong commitment and adaptability, principals’ agency is constrained by policy overload, unclear messaging, and limited meso-level infrastructure. The interpretive space between policy and practice emerges as the site where much of the most important curriculum work occurs and where leadership makes a critical difference. Principals are not passive recipients of change but active agents who filter, shape and, at times, challenge system messages and frameworks. This study makes a theoretical contribution by repositioning school leaders as key meso-level curriculum actors and by reconceptualising the meso layer as a relational and interpretive space. It offers practical and policy recommendations to strengthen system coherence, regional collaboration, and leadership sustainability through intermediary supports, professional learning and curriculum processes that are dialogic, trust-based and anchored in shared purpose. Ultimately, if principals are to act as effective mediators of curriculum change, their leadership must be systemically recognised, supported, and positioned as central to the success of meaningful and sustainable curriculum change.