A theoretical model of information technology (IT) project management was formulated based on the results of previous studies incorporating transactional and transformational leadership styles, team diversity, and team culture as determinants of team processes and project outcomes. The study addresses the lack of previous studies of IT projects and is concerned with infrastructure and software projects conducted in cross-functional environments with co-located teams in the context of Thailand. The model was tested and developed to a final model using data collected from a sample of 219 professionals with experience in IT projects in Thailand. The results confirmed several reported effects of leadership styles, team diversity, and culture on team cooperation, cohesion, and conflict and their subsequent effects on performance and psychosocial project outcomes. The findings highlighted results not commonly reported in previous studies of IT project management concerning the role of dominant cultural characteristics of Thai society at the level project teams as well as important direct effects of leadership styles and aspects of team diversity on performance and psychosocial outcomes. Based on the findings practical recommendations for improving IT project outcomes are presented.