Implementing measures by the European countries within the framework of the ratification of the Paris Climate Agreement should ensure an enlarged share in energy production from alternative energy sources and the introduction of new alternative energy capacities, which would provide an annual decrease in carbon dioxide emissions growth rate, reduce anthropogenic pressure on the natural environment and the use of non-renewable natural resources while preserving biodiversity. This paper aims at forming a system of indicators of sustainable transformation of the energy sector and studying their influence on the policy of environmental-oriented development. The paper applies Ward's method for determining the optimal cluster number and discriminant analysis for checking which variables significantly influence the formation of countries' clusters. The six clusters of countries obtained describe the different features of decarbonisation and climate change mitigation policies. Using discriminant analysis helped to single out the most relevant indicators of the energy sector's transformation in the direction of its decarbonisation and climate change mitigation. The most significant indicators (energy efficiency, electricity production capacities for renewables and wastes, and share of energy from renewable sources) largely determine the pace and features of forming sustainable development strategies for the energy sector. By highlighting the relevant cluster groups in the study, their characteristic features, and ways of transformational processes in the energy sector were discovered. This enabled the authors to form specific directions for strengthening and activating the processes of decarbonisation of the energy sector and climate change mitigation. There outcomes can become the basis for further research and the formation of appropriate strategies for sustainable development and transformation of the energy sector. The results stemming from this study could help scholars and other affiliated persons determine future strategies for research for implementing Sustainable Development Goals 2030.