In the current changing career landscape, the importance of career sustainability is becoming increasingly important. However, few studies have focused on the antecedents of leadership, especially from the strength-based approach. Both the strengths that are brought by the leader or by the individual themselves (e.g., protean career orientation) are key factors for the individual career development process. Based on strengths-based inclusive work theory, we argue that strengths-based leadership promotes career sustainability by bringing such strengths as career adaptability to the individual, especially when protean career orientation is lacking. We tested our moderated mediation model through a three-wave survey. Results show that strengths-based leadership is positively related to career adaptability, then further leads to career sustainability. Especially when protean career orientation is low, the relationship between strengths-based leadership and career sustainability will be amplified through the mediating role of career adaptability. We conclude that strengths-based leadership infuses individuals with more adaptability resources in situations where their strengths are insufficient, thereby promoting sustainable careers. Meaningful insights are provided for the domain of career development and leadership.