This study develops a research model of how and when high performers bring about constructive changes at work. Drawing from the social cognitive theory of self-regulation, we examined the mediating effect of role breadth self-efficacy (RBSE) on the relationship between task performance and taking charge. Moreover, we investigated the moderating effects of two forms of interpersonal hostility in the workplace (abusive supervision and group coworker undermining) on this mediated relationship. We conducted a field study and an experiment to test our theoretical model. Across both studies, the results showed that RBSE mediated the positive effect of task performance on taking charge. Group coworker undermining moderated the positive relationship between task performance and RBSE. The results also supported the moderated mediation effect of task performance on taking charge via RBSE contingent on group coworker undermining. We discuss the theoretical and practical implications of managing high performers to initiate constructive changes.