This paper illustrates the development, up to prototype stage, of an electromechanical actuation system for a medium-voltage vacuum contactor. Such development is carried out using a multi-domain simulation-based mechatronic approach, i.e. developing coordinated sub-models for the mechanism linking the actuator to the movable parts of the interrupter, the rotational electromagnetic actuator, and the power and control electronic circuit supplying the actuator and governing the system via a digital control unit. After a preliminary analysis, the modeling, design and check of the parts via coordinated simulations is presented. A prototype of the system, manufactured to validate the design procedure is finally presented.