How do episodes of transformational leadership transform followers? To address this question, we build on theories of affective events and affect regulation and develop a research model that explicates a mechanism of the transformation process implicit in transformational leadership theory. Specifically, the model explains how experiencing episodes of transformational leadership transforms (i.e., changes) followers’ positive affect and eventually their work engagement by fulfilling followers’ basic psychological needs. We tested our model in two independent longitudinal samples using daily and weekly measurement designs with 214 (N = 75) and 147 (N = 54) lagged observations, respectively. In support of our model, experiencing episodes of transformational leadership was associated with basic need fulfilment and led to a change in positive affect, which predicted changes in work engagement. Our findings suggest that a focus on affective dynamics can advance theories of leadership.