We developed and tested a model linking developmental experiences to leadership effectiveness and promotability through 2 mediating processes based on social cognitive and social capital theories. We hypothesized that a manager's exposure to 3 types of developmental experiences (formal development programs, developmental job challenges, and developmental supervision) would positively relate to supervisor's assessment of the manager's leadership effectiveness in the current job role and promotability within the organization through the manager's leadership self‐efficacy and size and quality of the manager's mentor network. Results based on a sample of 235 retail managers showed that leadership self‐efficacy and mentor network fully mediated the relationship between job challenges and promotability, whereas leadership self‐efficacy also fully mediated the relationship between job challenges and leadership effectiveness. Developmental supervision was indirectly related to promotability through mentor network. In addition, a 3‐way interaction analysis revealed that participation in formal development activities had a positive indirect relationship with leadership effectiveness and promotability mediated by leadership self‐efficacy when a manager experienced either lower levels of job challenge and developmental supervision, or higher levels of both. Our findings contribute to leadership knowledge by examining how both formal and informal developmental experiences relate to leadership effectiveness and promotability through social processes.