Contemporary satellite technologies in the fields of Earth Observation (EO), communications and navigation, augmented with terrestrial sensor networks, provide an invaluable toolbox for the development and deployment of integrated platforms for wide-area surveillance. The applicable use cases span across a wide range of application domains, from maritime and sea border surveillance to agricultural and environmental monitoring. This paper presents the design and development of a multi-mission service platform based on a generic core, able to aggregate data collected from multiple sensors and route monitoring information among processing modules and decision support systems. As the central point of a modular architecture, this service platform can be easily and quickly customized to serve multiple heterogeneous application domains. Its application for maritime surveillance is presented as an indicative use case.