Although mechanisms taking place prior to a leader training (LT) itself seem crucial for its effectiveness, public leadership scholars have so far rarely studied this pre-training stage. Drawing on Job Demands-Resources (JD-R) theory, this study aims to initiate this endeavor by identifying personal and job-related factors (i.e., resources and demands) that are linked to public leaders’ motivation to develop as a leader. Structural equation modeling reveals that predominantly public leaders’ self-efficacy, development needs perception and organizational support are crucial for their motivation to develop, which in turn is decisive for explaining public leaders’ willingness to participate in LT. This study theoretically contributes to a more comprehensive understanding of mechanisms underlying public LT and informs HR managers of potential levers to adequately support self-directed LT in public organizations.