This study has explored the Education for Sustainable Development (ESD) approach and implementation in six green schools in Sweden and Türkiye through a whole-school approach (WSA) lens. Interviews were conducted with nine teachers and three principals from each country. Based on the thematic analysis of the interviews, the authors reached four overarching conclusions that need to be developed in terms of integration of WSA to ESD in the green schools in both countries: 1) a comprehensive vision of sustainability; 2) an intrinsic view regarding purpose and pedagogy of ESD; 3) student participation across all aspects of the WSA; and 4) empowering an active community partnership. Furthermore, the research delved into the internal and external factors that either enable or hinder implementation of ESD within green schools. Drawing upon the case studies in two countries, the authors propose certain suggestions for the effective integration of WSA to ESD in green schools.