The sharing economy (SE) provides new opportunities to solve social, economic, and environmental problems, as well as increasing resource efficiency and releasing underutilized assets. However, social aspects of the sharing economy remain to be fully appraised. The present study aims to develop and apply a technique for assessing the sharing economy in the context of improving the social performance of smart cities. When considering social performance, we examine the relationship between the development of SE services and the public goods sector, as well as the potential of the sharing economy for improving the quality of life of citizens. A comparative analysis of approaches used to evaluate the sharing economy concluded that the social and environmental significance of the sharing economy can be most appropriately considered at the level of cities. The proposed technique is based on the use of the Smart City Index and Sharing Economy Index databases, data on collaborative economy platforms presented by Eurostat. The methodology used to assess the sharing economy comprises three stages: substantiation of the selected indicators for assessing SE; calculation of the presented integral index of the sharing economy; and construction of a matrix of indices of the sharing economy. At the first stage, correlation analysis was used; at the second stage, the TOPSIS system analysis method was used; and at the third stage we used graphical analysis. As a result, a ranking of 31 European cities was compiled in terms of the level of development of the sharing economy. It is shown that the sharing economy has a greater impact on public goods in cities with lower rates of economic development. In addition, significant changes in the 2020 ranking occurred due to restrictions caused by the COVID-19 pandemic. It is hoped that the obtained results will contribute to the development both of sharing economy methodologies and the urban environment by supporting sharing services.