Today, many cities in post-industrial societies are strongholds of left and progressive political forces. Almost 100 years ago, left parties had instituted municipal socialism in several European cities. In this article, we compare these two periods of left urban rule by focusing on the long-term changes over the last 120 years in the socio-demographic profile of urban left elites in four major Swiss cities. Our analysis of left elected representatives at six key dates highlights the main differences between the municipal socialists of the interwar period and the new urban left that rules contemporary cities. The former are members of the working class, blue-collar workers without university education, while the latter are members of the upper-middle class, highly educated sociocultural professionals. The results of our analysis contribute to a better understanding of the sociological composition of urban left-progressive political forces, an aspect that is somewhat neglected in recent research on the urban left. We discuss the potential political implications and further research avenues for contemporary debates in urban studies, in terms of urban policy priorities and political mobilization.