Background/purpose: Effective supervision is critical for credible educational quality assurance, yet a validated framework for External Quality Assessment Supervisory Units (EQASUs) remains absent in Thailand. This study aimed to develop and validate a competency framework of components and quality indicators to address this gap and enhance EQASU effectiveness. Materials/methods: The research was conducted in two sequential stages, in which the first stage used 18 experts to analyze the framework's core components and indicators. Second, the model was empirically validated through a survey of 434 external quality assessors (EQAs) in 2023, selected via proportional stratified random sampling. Data were analyzed using Confirmatory Factor Analysis (CFA) to validate the construct and the Mann-Whitney U test to examine performance differences. Results: The validation process confirmed a framework of four core components: organizational management (OM), personnel performance development (PPD), productivity and results (PAR), and cooperative networks (CN). All components demonstrated strong predictive power on EQASU effectiveness, with PPD emerging as the most crucial ([beta] = 0.94), followed by OM ([beta] = 0.81), CN ([beta] = 0.79), and PAR ([beta] = 0.78). A meta-evaluation of the framework's application confirmed the feasibility of its policy recommendations. Among the evaluation dimensions, utility was highest, followed by feasibility, accuracy, and propriety. Furthermore, high-performing EQASUs showed a significantly closer fit to the validated framework than the general group at the 0.01 level. Conclusion: The verified EQASU framework addresses a critical need in the Thai educational landscape. It contributes to the literature on assessment supervision and offers a practical, evidence-based tool for strengthening external quality assurance in Thailand and similar international contexts.