This paper examines and extends the theory of information systems success in the context of large-scale disaster management (DM) for public safety. In the recent past, various evaluation reports on DM efforts have concluded that information quality and system quality are major hurdles for efficient and effective multi-agency DM and are critical antecedents for information systems (IS) success. In contrast to the wealth of literature on IS success in profit-oriented business environments, research regarding drivers of public sector IS success is scarce. This research develops and empirically tests a model that explains IS usage intention as a reflective measure of IS success in the public sector DM domain. In this paper, the effects of the expected value of IS for the entire group of collaborating DM agencies, task support, user satisfaction, and three specific information/service quality dimensions on usage intention are examined. Data was collected from emergency responders using a questionnaire survey method during multi-agency, cross-national DM exercises at the Dutch–German border. The results of the data analysis revealed that expected group value is a key determinant of intention to use in the public sector DM domain. The data analysis also showed that perceived task support only has an indirect effect, through user satisfaction, on the usage intention. These findings imply that previously suggested IS success models for business environments are likely to fall short in their explanatory power and applicability for highly volatile complex disaster environments that require immediate coordinated responses from a large number of organizations. Possible directions for future research are also discussed along with other findings and implications.