The primary objective of this study was to understand the role of PMO and examine its impact on project performance. The secondary research explores the concept, various models and functions of PMO that are established in the organisations. The paper presents with a broad discussion on project success and failure rate, the role of project management, programme governance and the rationale behind establishing the PMO. PMO serves many functions and they are classified in 3 organisational categories: Standards organisation, Consulting organisation and Knowledge organisation. The research explores the role of the PMO in aligning projects with the business strategy and linkage or relationship between the PMO functions and project success criteria. Qualitative and Quantitative data collection methods are used to collect the primary source of data for this research. Research findings correlate with both the primary and secondary sources of data to evaluate the impact of PMO on project performance. Impact on each critical success factor (CSF) is examined separately for the organisations with PMO function and for those with no PMO function. The findings strongly suggest the influence of PMO in successful project outcomes. PMO aligns project activities with strategic objectives and impacts positively on project success. The thesis also identifies areas of further research and the personal learning of the author during this research project.