In contributing towards the discourse on developing teachers’ capabilities for Education for Sustainable Development (ESD), this study examines the relationships between sustainability knowledge, readiness, and self-efficacy for teaching sustainability concepts among vocational teachers in Malaysian colleges. Grounded in Bandura’s self-efficacy theory, the research assesses the combined effect of teachers’ sustainability knowledge and readiness on their ability to teach sustainability effectively. Using a cross-sectional survey design, a sample of three hundred and seventy-five (375) vocational college teachers and structural equation modeling (SEM), the results indicate no significant link between teachers’ sustainability knowledge and their readiness for ESD. However, a positive relationship between teachers’ readiness and their self-efficacy was found. The study shows that while sustainability knowledge does not directly enhance readiness for ESD, it is a strong predictor of self-efficacy in teaching sustainability. Moreover, readiness has a greater effect on self-efficacy than sustainability knowledge alone, highlighting the importance of conceptual understanding in building teachers’ confidence and competence in sustainability education. Despite focusing specifically on Malaysia and using self-reported data, which to some extent limits the study’s findings, the outcomes offer practical insights for educational policymakers, vocational institutions, and educators. They underscore the need for a comprehensive educational approach beyond just knowledge transfer. This research contributes to the sustainability education discourse and suggests areas for future studies, including exploring contextual differences and adopting longitudinal study designs to better understand the dynamics between sustainability knowledge, readiness, and teaching self-efficacy in vocational education.