The positive role of transformational leadership for productivity and mental wellbeing has long been established. Transformational leadership behavior may be particularly suited to navigate times of crisis which are characterized by high levels of complexity and uncertainty. We exploit quasi-random assignment of employees to managers and study the role of frontline managers' leadership styles on employees' performance, work style, and mental well-being in times of crisis. Using longitudinal administrative data and panel survey data from before and during the Covid-19 pandemic, we find that the benefits of different leadership styles depend on the environment: Employees of more transactional managers outperform those of more transformational leaders before the onset of the pandemic. During the pandemic, however, more transformational managers lead employees to better performance and mental well-being. We discuss potential explanations and implications.