Purpose This study developed and tested a multilevel moderated mediation model where transformational leadership was posited as the independent variable, teacher knowledge sharing as the outcome variable, psychological climate as the moderator, and teacher trust as the mediator. Design/methodology/approach Data derived from 962 teachers across 71 lower and upper secondary schools in Türkiye were analysed using structural equation modelling. Findings The results showed that transformational leadership influenced teacher knowledge sharing indirectly through teacher trust, and this indirect relationship was significantly moderated by psychological climate. Originality/value This study extends prior evidence by showing that the relationships between transformational leadership, teacher trust, and knowledge sharing are contingent upon the degree to which a psychological climate is established in schools.