Based on the concept of action competence, the current study introduces an integrated framework of Professional Action Competence in Education for Sustainable Development (PACesd) described by three defining features: willingness, knowledge of pedagogical approaches, and self-efficacy. To validate this framework, we developed a questionnaire measurement instrument: 'PACesd-Q'. This questionnaire was administered to a sample of 557 primary and secondary school in-service teachers in Flanders, Belgium. The instrument's psychometric quality was assessed in terms of its reliability, construct, and criterion-related validity. Results of reliability analysis and hierarchical (second-order) confirmatory factor analysis provided evidence of good measurement properties of the instrument in terms of reliability and construct and criterion-related validity. We suggest the instrument can be successfully used to provide educational practitioners with a tool to monitor and eventually identify professional development needs regarding education for sustainable development.