This article explores preschool principals’ leadership agency when enacting a new curriculum, looking at how they perform their role, how they organise their work and what challenges they face in the process. Drawing on the concept of agency, this case study focuses on the principals’ positions, practices, opportunities and limitations as well as their construction of agentic leadership. The data collection consists of in-depth, semi-structured interviews with 16 preschool principals working in a large Swedish municipality. The analysis of the material has taken place through thematic coding and interpreted through the lens of agency; the results show how the cultural, structural and material aspects of each preschool influence the enactment of the curriculum and shape the principals’ agentic capacity. Both time and context provide a framework for these principals’ enactments of a new curriculum within the specificities of their particular preschools and their own ambitions for the future. The principals’ discursive positionings are both filtered through these aspects and constructed on the basis of values and ideas about their own role and the role of staff. In addition, they underpin how the principals describe themselves as leaders and how they view their opportunities to act in an agentic manner.