To examine the relationship between organisational agility and nurses' green work behaviour and to assess how climate activism mediates this relationship. Understanding this relationship is crucial for promoting sustainable practices in healthcare. A cross-sectional research design was employed. This approach was chosen to examine how organisational agility and climate activism simultaneously influence green work behaviour in the present context, providing a snapshot of their synergistic interactions. This study was conducted in 2024 at eight hospitals in Egypt, with a total of 781 nurses conveniently selected for participation. Data were collected using validated instruments: the Agility Survey, Employee Green Behaviour Scale and Environmental Action Scale. Correlation and path analyses were utilised to test the study hypotheses. Nurses reported moderate levels of organisational agility, climate activism and green work behaviour. Statistically significant positive correlations were found between organisational agility, climate activism and green work behaviour. Organisational agility and climate activism emerged as significant predictors of green work behaviour, with climate activism acting as a partial mediator between organisational agility and green work behaviour. This study contributes to the growing body of knowledge on fostering sustainable nursing practices as results indicate that agile organisations, which embrace flexibility and nurse-led climate initiatives, are better positioned to promote sustainable behaviour. Practical strategies include selecting nurses with high climate literacy, designing agile working strategies and promoting eco-conscious behaviours. Nurse leaders should develop policies that integrate climate initiatives into everyday practice to enhance green work behaviour. The healthcare sector faces increasing environmental challenges, making it crucial to foster green work behaviour. Our study addresses a gap in the literature by revealing that organisational agility and climate activism are essential drivers of green behaviour among nurses, offering actionable insights for greening healthcare practices. This study was reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE). No patient or public contribution.