This study examines the impact of the project governance in post-merger integration projects on the overall performance of merger and acquisition transactions. To explore the impact, a research model was developed based on the extant research on the subjects of mergers and acquisitions, post-merger integration, and project governance. The model incorporates the structural elements of project governance typically used in practice and their underlying attributes, as well as measures of transaction performance—achievement of the synergies. Data collection was performed with the help of a self-administered online survey. It was found that elements of project governance are frequently used in practice of post-merger integration: Integration Steering Committee was present in 68% of the cases, Integration Manager in 63%, and Integration Management Office in 47%. As to the combinations of the project governance elements, full set of all three structural elements—Integration Steering Committee, Integration Management Office and Integration Manager was the most popular combination and present in 36% of the cases. A large number of cases had no formal project governance implemented at all—17%. Presence of all three structural elements was found to be associated with better overall transaction performance related to the synergies of both top line growth and costs. Transactions that had all three structural elements at the integration stage outperformed the ones without any formal project governance. Most importantly, the average deal performance increases from not meeting the expectations to meeting or slightly exceeding them for the cases with all three structural elements present. At the same time, formal project governance implemented with one or more of the structural element missing does not produce a significantly different performance from the cases without any formal project governance at all. Further, it was established that better fulfillment of the roles of Integration Manager and Integration Management Office as defined by a combination of various attributes could be clearly associated with the overall transaction success. In case of Integration Manager, there was a weak positive statistically significant correlation observed with both synergies of top-line growth and synergies of cost. For Integration Manager, the same was observed but at a very weak statistically significant level. Notable attributes for the Integration Manager were related to the personnel authority and project authority, while for the Integration Management Office positioning within the organization was more important. The limitations of this study include sampling, self-selection, non-response, socially desirable answers, and possibly inaccurate recollection of events and inaccurate assessment of past M&A deal performance by the respondents. The unique contribution of this study is in providing evidence of the value of project governance in post-merger integration context via achievement of transaction synergies.