Socio-environmental challenges such as climate change and biodiversity loss necessitate political action and transformative educational responses. Education for Environmental Citizenship (EEC) offers a promising framework for addressing these issues in school settings. However, there is a lack of reported structured teacher professional development (TPD) programmes that support EEC. This study presents a systematic literature review (SLR) of empirical studies and supranational frameworks, synthesising the results into a model for in-service TPD in EEC. The analysis identified core competencies such as critical thinking, systems thinking and global citizenship alongside with dimensions including socio-emotional and cultural-territorial competencies, which address context-specific educational needs. These are mapped to pedagogical strategies such as outdoor learning, reflective practice and community-based learning. The resulting model seeks to align global sustainability goals with local realities. This research lays the groundwork for fostering EEC by providing educators with the competencies and strategies essential to drive social and environmental change.