Objective: School-based prevention interventions informed by the World Health Organization Health Promoting School (HPS) framework aim to improve the health and wellbeing of school-aged children, yet few studies describe factors influencing the successful implementation of this framework in secondary schools. This study sought to explore why and how secondary schools might implement the HPS framework and factors contributing to success. Design: Qualitative case study. Setting: A single secondary school in Victoria, Australia, purposefully selected due to local recognition of an HPS policy. Method: Data collection included semi-structured interviews, document retrieval, drawings and ethnographic observation. Data were analysed using framework analysis. Results: The school had elected to implement the policy as it aligned with its existing health and wellbeing policy framework and provided a flexible yet evidence-based framework to guide a whole-of-school approach to promoting health and wellbeing. Success was perceived to be dependent on selecting easier health priority areas to address initially, the allocation of a designated team to guide policy implementation and access to a skilled health promotion worker to assist implementation. Conclusion: Study findings highlight potential reasons why and how secondary schools might implement the HPS framework and factors contributing to success. Further research is warranted to enhance the transferability of these findings and explore the impact of the HPS framework in secondary schools.