At present, scientific and technical activities (STA) play a fundamental role in the creation of new knowledge necessary for the realisation of the goals of sustainable economic growth. The purpose of the research is to assess STA in countries of the world and Ukraine as well as to analyse the impact of STA on their sustainable economic growth. For the assessment of STA of world countries, we have developed a composite indicator (Index of STA–ISTA) based on two sub-indices (Potential of STA and Results of STA) and a set of partial indicators. The study is carried out using a theoretical and methodological approach that includes five research stages: calculating the ISTA of world countries with their subsequent ranking; assessing the impact of the ISTA on the economic growth of world countries; evaluating the correlations between the ISTA, the Global Innovation Index (GII), and the Human Development Index (HDI); breaking down world countries into groups with the help of cluster analysis, using data on the ISTA, GII, HDI; assessing and analysing the importance of environment-related technologies and innovations in ensuring the economic growth of countries of the world. According to the results of the study, the importance of STA in ensuring sustainable economic growth of countries of the world was confirmed. The use of cluster analysis to group countries of the world in terms of the level of STA made it possible to identify three clusters of countries: leaders, potential leaders, and catching-up countries. It has been proven that in order for a country to achieve leadership in terms of STA, it is important to harmoniously combine efforts to support and develop its scientific potential as well as to create principles for the implementation of scientific achievements in innovation activities to ensure its economic growth and improve the living standards of its population. Besides, the analysis allowed proving the existence of a moderately positive impact of the development of environment-related technologies and innovations on the acceleration of innovative development, improvement of the quality of life of the population, and the growth of GDP per capita.