Universities are increasingly expected to contribute to societal and environmental challenges, yet the concept of the fourth mission remains fragmented and weakly operationalized in the literature. This study aims to develop a measurement framework for the fourth mission of universities. The research adopts a theory-driven qualitative design based on a systematic literature review, synthesizing contributions on community engagement, social innovation, sustainability and institutional embeddedness. Building on this synthesis, the study develops a three-level conceptual model that integrates an institutional framework, core fourth mission processes and transformative impact domains. The core processes are structured around community engagement, co-creation and social innovation, and knowledge diffusion and local application, while the model explicitly links these processes to societal challenges and environmental sustainability outcomes. Furthermore, the model is operationalized through a structured indicator system applicable in document-based analysis, supported by a four-point scoring scale capturing the depth of institutionalization. An illustrative pilot test was also conducted using the example of one university faculty. The study contributes by clarifying the boundaries of the fourth mission and offering an operational framework that shifts attention from output-based measurement to universities’ transformative societal roles.