Current generation of distributed real-time systems requires more flexibility andthe ability of changing its behaviour at run time. This paper presents a model and an algorithm for QoS-aware service composition in distributed systems with real-time requirements. This model is applicablein application domains where temporal guarantees and flexibility are needed, such as remote monitoring, control or surveillance.Our approach combines concepts from the service oriented paradigm and distributed real-time systems. We propose a concrete system model based on a holistic time-triggered-based approach for design and configuration andtwo composition algorithms: an exhaustive one that computes the optimal service combination in terms of a figure of merit, suitable for off-line composition; and a distributed one, based on heuristics, that can be used for on-line distributed composition.