In this study, we assess plausible decarbonization pathways in Colombia using an open-source national energy system optimization model (OSeMOSYS). We build three scenarios over 2021-2050 and contrast them in terms of emissions, energy consumption, technology deployment, costs, and benefits. The results show that a decarbonized energy system can reduce carbon intensity by 93%, energy intensity by 44%, fossil fuel imports by 90%, and provide socioeconomic benefits equivalent to 21% of the Colombia's 2021 GDP. We use these results to recommend milestones and policy actions that can help inform policymakers about cost-effective strategies to achieve a sustainable, efficient, and more resilient energy system by mid-century. Our transparent and systematic methodology provides a tool for long-term energy planning in Colombia which can also be replicated in other developing countries for assessing decarbonization pathways.