This paper presents the development and testing of an impact assessment tool for the Cities2030 project aimed at transforming city-region food systems to align with the European Union’s Food2030 policy and the European Green Deal. This study highlights the importance of sustainable urban food systems, focusing on food security, environmental sustainability, and public health. Using a design thinking approach, this research emphasizes co-creation, stakeholder engagement, and iterative refinement, developing a flexible, multi-dimensional framework adaptable to diverse city-region contexts. Through collaboration with 65 stakeholders, this tool was tailored to meet the socio-economic and environmental needs of different regions. Case studies from Cities2030 partner cities demonstrate its effectiveness in fostering cross-sectoral collaboration, enhancing community participation, and driving food system innovations. Key findings reveal measurable impacts across social, environmental, and economic dimensions, while addressing challenges like regional disparities in data collection and the need for improved long-term tracking of sustainability metrics. This study concludes by underscoring the role of adaptive, inclusive strategies in assessing urban food systems’ sustainability and resilience and suggests that the tool’s framework could be applied to other urban sustainability areas, such as energy and water management.