In these competitive and turbulent times, project organisations face severe challenges. Despite the advancement of project management tools and techniques, the rate of project failure exceeds that of success. Regardless of calls for further empirical studies on the role of project leadership, researchers struggle to find the best leadership styles for project success. New digital transformation phenomena have forced organisations to offer more autonomy and decision-making authority to those at lower hierarchical levels. In this scenario, top management support plays a facilitator role. To the best of the researcher's knowledge, no past studies have examined these critical project success factors simultaneously in a project environment. Embedded in the theories of contingency, goal-setting, and social cognition, this study raised the hypothesis that project managers’ leadership styles impact project success via the mediation of goal clarity, empowerment, and self-leadership as well as the moderation of top management support. Data was collected by administering a cross-sectional survey to 289 project organisations in the IT sector. The results demonstrated that project managers' transactional leadership style does not impact project success because goal clarity has an insignificant association with project success. However, the transformational leadership style showed a positive impact on project success because empowerment significantly and positively relates to project success. The project manager's empowering leadership style was also found to positively influence project success through followers’ self-leadership. Additionally, top management support revealed a significant moderating role by strengthening the relationship between empowerment and project success. This study successfully fills theoretical gaps by introducing a novel moderated mediation model. The findings also offer useful insights to practitioners by revealing that project managers’ transformational leadership and empowering leadership are needed to enhance and encourage employee empowerment and self-leadership, and ultimately secure project success.