Project-based organisations face the challenge of persistent project failures, leaving researchers and practitioners struggling to identify the best leadership style for project success. Data was collected from 289 project organisations and analysed to reveal that the project manager's transformational leadership behaviour and empowerment significantly improve project success. Additionally, empowerment mediates the impacts of transformational leadership and goal clarity on project success. Goal clarity was found to mediate the relationship between transformational leadership and empowerment, but not between transformational leadership and project success. Lastly, contingent reward leadership does not moderate the effect of empowerment on project success. The findings have theoretical and practical implications in the project management field.