This study explores the role of idiosyncratic developmental deals (i-deals) in shaping the career of employees. The study tests how employees use i-deals to influence promotability decisions legitimately. The study proposes that i-deals develop new skills through the developmental challenge to navigate future growth. Since proactive employees are more likely to negotiate developmental i-deals to obtain developmental challenge, the study evaluates the moderating role of proactive personality. Strong performance in a developmental challenge influences promotability decisions as it signals what employees can do. Multi-source data were collected from junior mangers and their supervisors at different time points from a large information technology organization based in India. Data analyses comprised of regression analyses to test the hypotheses followed by process modeling to examine the conditional indirect effects was conducted. The results indicate the moderating role proactive personality between developmental i-deals and developmental challenge. Additionally, developmental challenge mediates the moderation effects of proactive personality, thereby, confirming the mediated moderation. The study highlights the implications for i-deals and personality research.