Purpose: Principals' well-being worldwide is under increasing threat due to the challenging and complex nature of their work and growing demands. This paper aimed at developing and validating a multidimensional Principal Well-being Inventory (PWI) and examining the state and consequences of principal well-being. Design/methodology/approach: This paper involves four independent samples of principals working in schools from Hong Kong and Mainland China. The research design consisted of four phases with four sequential empirical studies. Phase 1 was to establish the content validity (literature review and Study 1); Phase 2 was to test the construct validity (Study 2 and Study 3); Phase 3 was to build the criterion validity (re-use the data from Study 3) and Phase 4 was to test the cross-validity of the PWI (Study 4). Findings: Based on published literature and four successive empirical studies, a 24-item PWI was created via a theoretical-empirical approach of test construction. Validity was confirmed through construct-, content-, criterion- and cross-validity testing. The PWI covers the six important well-being dimensions -- physical, cognitive, emotional, psychological, social and spiritual -- to present a general picture of principals' occupational well-being associated with job nature, well-being literacy, leadership and context. Research limitations/implications: The inventory will aid efforts to promote principal well-being as an essential component of schoolwide well-being, quality education and a wellness society. Practical implications: During the post-COVID-19 period, this project is deemed both critical and timely so that quality education will not be sacrificed due to factors affecting principal well-being. Originality/value: This theoretically and empirically validated inventory serves as a robust tool for comprehensively understanding principal well-being and a fuller exploration of their well-being literacy, drivers and outcomes.