Despite of the huge investments in information technology (IT), IT project success rates are unsatisfactory and still remain very low. This issue has been investigated by many researchers all over the world to identify the critical success factors. However, there is no universal agreement on which factors are significant to success. This paper presents an investigative study of the main factors that affect IT projects success in Saudi Arabian public organizations. A two-phase approach has been adopted combining qualitative and quantitative research methods. In phase I, a qualitative approach using semi-structured interview method was used to collect and analyze the data, and the findings of this phase proposed seventeen factors. Then, in phase II, a quantitative approach using questionnaire method was used to assess and validate the outcomes of phase I. The findings of the questionnaire confirmed the importance of those seventeen factors, and the critical success factors (CSFs) of IT projects in Saudi Arabian public organizations to be found are: top management support and commitment, project management, project team competency, communication management, strategic planning, training and education, partners and suppliers management, and stakeholders management.