The current paper aims at developing and validating a Teacher Leadership Inventory (TLI). Adopting the theoretical-empirical strategy of instrument development, the procedure consisted of taking a sample of panel experts and undertaking six sequential empirical studies with sufficient samples of teacher leaders from China. After verifying content validity, structural validity, criterion validity, and cross-validity, a 25-item multi-dimensional model on teacher leadership behaviours with five factors was identified. The resulting TLI could provide a validated instrument for future research investigating the nature of teacher leadership behaviours as an independent construct and their relations with other relevant constructs. It is expected that the TLI could serve as a more robust means for promoting the research and practice of teacher leadership.