Although a myriad of studies have examined the role of social networks in employment, little attention has been paid to their impact on career outcomes, such as promotion. This paper therefore examines how connections with senior prosecutors with a successful career outcome affect the probability of promotion for junior prosecutors in South Korea. To identify a causal network effect, I exploit exogenous variation in networks arising from personnel transfer assignments. The result shows a positive effect from connections with successful seniors: a one standard deviation increase in the number of connections with successful seniors increases the probability of being promoted for a junior by 10.1 percentage points. Here, I evaluate the importance of three potential mechanisms: (1) skill spillovers from a senior to a junior, (2) transmission of information on a junior’s performance between seniors, and (3) nepotism based on alma-mater connections. Empirical evidence consistently points to transmission of information as a major potential mechanism facilitating network effect. Skill spillovers and nepotism also play a meaningful role in determining a junior prosecutor’s promotion. My findings thus suggest that matching a successful senior with a junior in minority groups is an effective way of supporting advancement and representation of minority groups within organizations.