The contemporary process of economic development necessitates a heightened focus on matters of sustainability, with a particular emphasis on sustainable energy policy. This is of paramount importance for the protection of the natural environment and the achievement of long-term economic growth. In the context of countries such as the Czech Republic and Poland, which have historically relied on high-carbon energy sources, the transition to a more sustainable energy system represents a significant challenge. The objective of this paper is to undertake a comparative analysis of the trends in energy sustainability in the Czech Republic and Poland from 2017 to 2021, with a particular focus on key performance indicators. The analysis, based on data from the OECD database, revealed notable discrepancies in the rate of change between the two countries, with Poland exhibiting a more pronounced surge in the proportion of renewable energy sources (RES). A Student’s t-test confirmed the existence of statistically significant differences in key indicators between the Czech Republic and Poland, thereby underscoring the diverse challenges that both countries encounter in their pursuit of sustainable energy development. The Granger causality test was employed to ascertain whether variables exhibit temporal relationships that may suggest potential correlations. However, it is important to note that this test does not prove direct causality, but rather indicates that the variables are related at a specific point in time. Interpretation of the results must be undertaken with caution, as the test does not account for the full complexity of relationships between variables, including external factors and structural changes in the economy. Meanwhile, the LMDI decomposition analysis identified the principal drivers of alterations in CO2 emissions. The findings indicate that, despite advancements in sustainable energy development, Poland and the Czech Republic are confronted with distinctive challenges that necessitate the implementation of tailored policy responses. It is therefore recommended that further investment in renewable energy and the modernisation of energy infrastructure be made in order to achieve long-term sustainability goals.