Prior research has shown that an employee’s knowledge, skills, and capabilities are associated with leadership effectiveness. We contend that the evolving network of advice relationships that an employee is embedded in also affects leadership effectiveness. We develop a dynamic network theory of leadership effectiveness and address two key issues. First, how does an individual’s network of advice relationships influence their leadership effectiveness over time? Second, how does an individual’s leadership effectiveness influence how they develop their advice network? To answer these questions, we theorize that leadership effectiveness and advice networks are co-constituted. We build from a micro-foundations view of network agency and hypothesize that leadership effectiveness increases due to the reputational benefit of being a source of advice, and a contagion effect where individuals benefit by learning from colleagues with higher leadership effectiveness. Furthermore, we hypothesize that employees with higher leadership effectiveness build advice networks that enable further learning, and notably these advice ties cross intraorganizational boundaries. To test our theory, we gathered three waves of data from 158 employees in a consulting firm and conducted analysis using a stochastic actor-oriented model (SAOM). We find support for our hypotheses and finish by discussing the practice-oriented implications of our findings.