Project-based organizations (PBOs) have been widely recognized as powerful generators of knowledge and innovation owing to their autonomous, multidisciplinary, and goal-oriented operations in the form of projects. However, evidence shows that PBOs are likely to suffer a knowledge flow gap between operational and strategic management levels leaving much of PBOs’ knowledge trapped within project boundaries. Although several studies advocated the use of project management office (PMO) to enhance the interaction between these levels, very few examined PMO knowledge brokering (KB) roles. This study therefore tries to synthesis theories and evidence around PMO KB roles to produce a theoretical understanding on how PMO managers mediate every knowledge flow transaction in PBOs. A theoretical model identifying three key levels of knowledge flow transactions, each of which is mediated by a set of KB roles, has been developed. The model heights the powerful potentials of PMO KB roles in governing PBOs’ knowledge by balancing bottom-up explorative with top-down exploitative knowledge flow transactions. Theoretical contributions, practical implications and future research directions have also been outlined as part of this study.