In recent years, while developed countries are decommissioning hydroelectric projects (HEPs)/dams at a higher rate than constructing new ones, developing economies are doing the opposite. Although HEPs are regarded green, renewable and cheap, recent studies reveal that they do more harm than good. The impacts of HEPs are multiple, including socio-economic, environmental and geopolitical. India’s Northeastern (NE) region is a part of the Ganges–Brahmaputra–Meghna river basin, and has immense hydropower potential. A large number of HEPs are planned or under construction in the region, mainly in the hilly states of Arunachal Pradesh, Manipur, Meghalaya, Sikkim and Mizoram. One such mega project is the Tipaimukh multipurpose HEP, to be constructed on the Barak river in the state of Manipur. The project is highly controversial, and is being protested against by the locals, academicians, researchers, social activists, NGOs, as well as Bangladesh. Further, a serious cost–benefit analysis, judicious environmental impact assessment and democratic public hearings have been questioned. The area submergence of the project is disproportionately high compared to other such projects of NE India, and the project site and the adjoining areas form a part of Indo-Burma global biodiversity hotspot. The present study details the impacts of the project from multidisciplinary perspectives, categorized into bio-physical, socio-economic and geopolitical impacts, including impacts on the downstream riparian nation—Bangladesh. Based on the study, we have provided recommendations, if ever the construction of project is actualized. Since there is lack of any such analysis, the present study is of immense significance on the decision making of the project, and paves a guideline for impact analysis of the upcoming large number of projects of the region.