The quality of life of citizens in a city is related to the sustainable decisions made by their leaders. By using principal component analysis (PCA) and taking an intellectual capital perspective (all sources of knowledge in human, relational and structural areas), we explore which of the three dimensions used to measure the sustainability of a city—economic, social or environmental—has the greatest effect on a subjective measurement of quality of life. We propose an econometric model based on a tangible production model to study the relationship between the quality of life and sustainability. To that end, we perform an in-depth examination of the different effects on the four dimensions that comprise the measure of the subjective quality of life: satisfaction, mobility, integration and public service. The results of the estimated model of citizens’ quality of life confirm the existence of a direct relationship for the 52 European cities under study; however, the least relevant role is played by the environmental dimension, which is still unappreciated by citizens. Conversely, the economic and social dimension are found to be determinants in all cases, except for social integration. Therefore, a key requirement of the management aimed at achieving sustainable development in European cities is to activate the environmental dimension.