This article addresses one of the contemporary economy’s most challenging endeavors: the energy transition. Specifically, the aim of the study was to assess the effectiveness of Poland’s energy transition process between 2004 and 2021. A comprehensive approach is employed to analyze Poland’s energy transition process, focusing on the effectiveness of implementation through the Energy Transition Effectiveness Index. This methodology incorporates four dimensions, namely energy security, economic considerations, climate impact, and social aspects, each characterized by 22 sub-indices. The research methodology employs a two-tiered approach based on the multi-criteria decision making methodology. The EDAS method is utilized to determine the indices’ values, while the CRITIC, equal weights, and statistical variance methods and Laplace’s criterion are employed to ascertain sub-indices values and dimension weights, particularly useful for decision making under uncertainty. Moreover, the relationship between these indices, the Energy Transition Effectiveness Index, and Poland’s Gross Domestic Product is explored. By evaluating Poland’s energy transition effectiveness from 2004 to 2021 and comparing the results with other European Union countries, it becomes evident that the effectiveness varies over time. Despite encountering economic and social challenges during the energy sector’s transformation, Poland exhibits positive progress in its energy transition efforts, outperforming certain European Union counterparts. However, there is a pressing need to intensify efforts to curtail emissions and enhance renewable energy utilization. The European Union’s support and coordination are deemed crucial in facilitating these endeavors, alongside fostering the wider adoption of best practices among member states. The developed methodology stands as a valuable tool for ongoing evaluation of transformation processes across European Union nations.