The current study extends past research by examining leader-member exchange as a mediator of the relationship between employee reports of psychological contract breach and career success. In addition, we tested a competing perspective in which we proposed that performance mediators (i.e., in-role performance and organizational citizenship behaviors) will mediate the breach-career success relationship. Subjective and objective indicators of career success were assessed using supervisor-rated promotability and archival data on actual promotion decisions, respectively. In Sample 1, we found that supervisor-rated leader-member exchange (T1) mediated the relationship between breach (T1) and objective career success after 2 years. In sample 2, we replicated and extended these results using a three wave measurement over three years. Specifically, we found that leader-member exchange (T2) mediated the relationship between relational breach (T1) and subjective (T2) and objective (T3) career success. Performance-based mediators at T2 were no longer significant when regressed together with leader-member exchange and relational breach, ruling out alternative mediator explanations. (Contains 4 tables.)