In this article, using a novel, annual cross‐country panel dataset that covers 160 economies from 1950 to 2016, we examine the association between the size of the informal sector and various indicators of sustainable development. The range of indicators encompasses health‐related, economic, environmental, education, and social variables. Our results suggest that the size of the informal sector is negatively associated with GDP per capita, carbon dioxide emissions per capita, education, educational attainment, life expectancy, and access to safe drinking water, and positively related to female labor force participation rate, poverty rates, mortality rates, and air pollution. We also find that these empirical associations significantly interact with GDP per capita, indicating that the effect of larger informal sector size is stronger in less developed economies.