This paper aims, through a longitudinal case study, to present and analyze the transitions in operational activities and the performance of a Project Management Office (PMO) in a technology-based company. The paper discusses functions, tensions, stakeholders' interfaces, performance and how they drove the major changes faced by the PMO. The changes in the PMO were mainly based on non-planned events rather than in a change of the management process. The results demonstrated that political tensions in the organization, rather than project management performance, explained the PMO transitions. Managers must look for identifying tensions in the project management environment, project performance and stakeholders' satisfaction in order to propose and direct PMO changes and the sustainability of project ongoing bestpractices. This study also contributes to the collection of evidences that corroborate previous literature appointments, as well as to question some results that need to be contextualized according contingencies for avoiding mimicry in the PMO implementation and transformation.