The present study tests a model of moderated mediation in the relationship between transformational leadership and follower emotional strain. Based on the job demands-resources model, we suggest that transformational leaders may be able to decrease follower emotional strain by providing social support. It is also proposed that a protective effect of social support from a transformational leader will depend on the employees’ level of professional ambition. Mediation by social support may be stronger for ambitious employees, such that transformational leadership may be associated with less emotional strain for these employees (moderated mediation). A sample of 199 employees participated in a cross-sectional study in Germany. Results confirmed the hypothesized moderated mediation indicating a health-promoting effect of supervisory social support for ambitious employees (not found for low levels of ambition). The study suggests that the idea of a general positive effect of transformational leadership on followers’ emotional strain is not appropriate.