Guaranteeing the correctness of the future system is of vital importance for the development of critical and complex systems. Rigorous software development methodologies are used for such systems, where formal methods for the verification of properties guarantee the required level of correctness. For process-centric, critical and complex systems, one needs continuous observation of the process (through simulation and visualization) both during the development for correctness and afterwards for process improvement. We present a framework with associated methodology and tools, for the development of process-centric critical and complex systems. This early validation methodology promotes formal verification of the process model alongside agent-oriented simulation and visualization of the process models in a distributed context. Moreover, the process simulation technique proposed in the methodology allows step-wise replacement of the simulated components with the actual system services. We explain the proposed methodology using an adaptation of a real-life case-study from the military sector.