Background Climate change is impacting the health of individuals worldwide. At the same time, the healthcare sector contributes to carbon emissions. In Australia, healthcare contributes 7% of the country’s carbon footprint. Research into the environmental impact and mitigation of carbon emissions in primary care is an emerging area. Objective To explore staff perspectives on facilitators and barriers to environmental sustainability in 3 Australian general practices seeking to reduce their environmental impact. Methods We used a qualitative, case-study approach, conducting 23 semistructured interviews with staff across the 3 practices including nurses, administrative staff, and doctors. Observation of systems and staff behaviour relating to environmental sustainability was undertaken at 1 practice. Thematic analysis was conducted to determine themes relating to factors influencing the implementation of environmentally sustainable initiatives within practice settings. Results Climate mitigation efforts raised by participants were largely focussed on energy and waste reduction, rather than prescribing pharmaceuticals and staff and patient transport. Three main factors influencing change towards sustainable practice were identified: “Leadership,” “Staff Engagement and Workplace Culture,” and “Concomitant Benefits.” A leadership team and workplace culture that valued environmental sustainability were found to be important facilitators, as were concomitant benefits, in particular financial savings. Barriers included what interviewees described as a lack of knowledge about initiatives with the highest impact, lack of understanding described by staff of the evidence behind particular initiatives, waning staff engagement and infection control concerns. Conclusions Our research highlights several important factors that contribute to the implementation of intended environmentally sustainable initiatives in these 3 practices. Further education, research and high-level policy guidance on the potential environmental impact of prescribing pharmaceuticals, staff and patient transport and unnecessary tests and treatments are recommended to further promote environmental sustainability in primary care.