Research suggests that innovative and engaging professional development is instrumental in supporting teachers in developing their competence and confidence in teaching sustainability. An international initiative was developed to explore whether a competencies-oriented Education for Sustainable Development (ESD) professional development model was transferable across three different international contexts (Ireland, Germany and Mexico). This paper reports on the adaptation of this model within the Irish context, through the development of an innovative professional development programme for primary teachers. Through a mixed-methods approach which gathered data via pre- and post-programme surveys, teachers' reflective journals and post-programme group interviews, the paper explores Irish primary school teachers' experiences of, and attitudes towards, teaching sustainability through science education after participation in a professional development programme. The findings suggest that this programme, structured around the existing evidence for effective professional development in science education and ESD, positively influences teachers' self-efficacy, supports teachers' critical engagement with sustainability competencies and promotes the development of transformative pedagogies for sustainability through Inquiry-Based Science Education.