We seek to better understand how formal mentoring may impact protégés’ leadership development by arguing that protégés’ informal mentoring networks help explain the relationship between formal mentoring and two protégé leadership development outcomes: motivation to lead and promotability. We also argue that protégés’ political skill and gender serve as boundary conditions of these mediated relationships. Using 100 South Korean mentor-protégé dyads in four organizations across three points in time, we find that a higher level of formal mentoring is positively associated with the quality of protégés’ informal mentoring networks, which, in turn, is positively associated with protégés’ motivation to lead, but not protégés’ promotability. We also find that the relationship between a higher level of formal mentoring and the quality of protégés’ informal mentoring networks is strengthened when protégés have a higher level of political skill. In addition, we find that female protégés obtain more informal mentoring networking benefits from their formal mentors than male protégés. Theoretical and practical implications are discussed.