The paper contributes to two research gaps: (1) The need for knowledge on key urban form characteristics promoting the scale-up of car sharing services in a sustainable way, (2) The need for practical approaches in the dialogue between key private and public actors introducing or expanding car sharing in local contexts. These requirements are addressed through a Finnish case study in two locations. By combining car sharing use data, monitoring data on urban form and mobility patterns, and stakeholder interviews, we present a novel approach to promote sustainable car sharing. The approach widens present knowledge on the sustainability potential, role and business potential of shared mobility in future urban transport systems. It also provides a tool for cooperation among urban and transport planners and car sharing providers. Our analysis shows that well-designed car sharing services can provide a sustainable and agile opportunity for the mobility demand of urban residents. However, achieving sustainability demands requires systematic and integrated user profile, daily mobility, and urban form analysis enforced equally by the city or municipality and private service providers.