Leadership behavior is associated with leader well-being. Yet, existing research, with the majority representing cross-sectional studies, limits our understanding of the association over time, potential mediating mechanisms, and potential reciprocal relations. Based on Conservation of Resources (COR) theory, we test between- and within-person relationships between transformational leadership and leader vigor as well as emotional exhaustion over time. In addition, we include leaders’ occupational self-efficacy, information exchange with followers, and meaning of work as mediators. 132 leaders participated in a fully cross-lagged study across three consecutive weeks. We analyzed the data with a random intercept cross-lagged panel model (RI-CLPM) that allows separating the within- and between-person variance in our variables. At the between-person level, transformational leadership was positively related to vigor, occupational self-efficacy, information exchange, and meaning of work. At the within-person level, there were no lagged associations of transformational leadership and well-being, but a positive lagged effect of vigor in one week on information exchange and meaning of work in the next week. Within one week, transformational leadership was related to occupational self-efficacy, meaning of work, and vigor (positive, respectively) and to emotional exhaustion (negative) within persons. In line with COR theory, we discuss transformational leadership as a resource for leaders associated with greater well-being for leaders. Our study contributes to the literature on dynamic leadership behavior and the mechanisms between leadership and leader well-being