In order to mitigate the climate change process, the European Union has adopted a European Green Deal, which foresees zero net emissions of greenhouse gases for all member states by 2050. This paper investigates the possibility of achieving a 100 % renewable energy system that would meet the requirements set out in this agreement. Montenegro was used as a case study to analyse different energy transition pathways. Two scenarios with different dynamics of integrating renewable energy sources in the energy system were determined for 2030, 2040, and 2050. Scenarios were simulated and analysed in the EnergyPLAN model. Due to the large potential in Montenegro, hydropower plants will have a significant share in the production of electricity, but special attention was given to the integration of variable renewable energy sources like solar and wind energy. The analysis shows that it will be possible to achieve a 100 % renewable energy system in both scenarios with the implementation of energy efficiency measures, energy storage systems, synergies with the transportation sector, and balancing through demand response.