In the last few decades Information Technology (IT) has grown manifolds in Pakistan. The dynamic organizations are continuously replacing their legacy systems with the contemporary information systems (IS). Particularly, Enterprise Resource Planning (ERP) systems are now becoming an integral part of the organizations to automate business processes. This thesis empirically investigated: (1) the success of ERP system at individual, process and organizational levels and (2) explored different contextual factors relating to organization, technology, individual and environment that affect the level of ERP system success in corporate sector of Pakistan. For examining ERP system success, the study applied DeLone and McLean (1992, 2003) (D&M) ‘Theory of IS Success’. The five dimensions mentioned in the theory and an additional dimension was incorporated in the proposed ERP system success measurement model i.e., ERP system quality, ERP information quality, ERP service quality, individual performance, organizational performance and process performance (added to the model). The present study applied two phased ‘explanatory sequential’ mixed methods research design. In the first phase of research 514 Pakistani organizations were surveyed through structured questionnaires to investigate ERP system success. SmartPLS 3 Software was used and Partial Least Square – Structural Equation Modeling (PLS-SEM) technique was applied for testing the study hypotheses and assessing convergent validity, discriminant validity and internal reliability of the constructs. The results from the first phase indicated that ERP system quality, information quality and service quality positively influence individual performance. Similarly, individual performance has also positive and significant relation with process performance and xix organization performance. The results also revealed that process performance has positive and significant impact on organizational performance in Pakistani organizations. Based on the findings from the first phase, qualitative research strategy was applied in the second phase of research to explore different contextual factors that affect the level of ERP system success in corporate sector of Pakistan. The qualitative data was collected through in-depth video recorded interviews of 48 ERP key users in four different organizations. NVivo 10 software was used for transcribing, coding and identifying different themes of the study. Word Tree, Word Tag Clouds and Tree Maps techniques were applied to identify frequency of data coding, talk pattern and significance of each contextual factor. Finally, the qualitative phase of research explored that rewards and incentives, training, leadership, management control, technological resources, up-gradation of technology, skills, knowledge, provision of electricity and stakeholders’ pressure are more critical factors that influence the level of ERP system success in Pakistani organizations. Thus, these findings suggest that organizations can enhance the level of ERP system success by controlling these contextual factors. Lastly, the both quantitative and qualitative results were discussed and different theoretical and practical implications were provided. The findings of the study will serve as changing driver of attention of the practitioners from the issues of pre-implementation or implementation stages to the issues of post-implementation stage of ERP system. Based on different results and discussions, practitioners will pay more attention to sustain the success of ERP system in their organizations. Keywords: ERP system, ERP success, DeLone and McLean Model, IT performance, Contextual Factors