Aging of population and increased incidence of gait impairments are dominant trends undermining social welfare and healthcare system. Lower-limb wearable robots proved to be a viable solution for recovering mobility of people affected by gait disorders. This work presents the design of the mechatronic architecture of a fully self-contained active pelvis orthosis (APO) for assisting hip flexion/extension movements during daily living activities. The APO could act compliantly with the human biomechanics thanks to series-elastic actuation and to a novel kinematics chain endowed with passive degrees of freedom. The portability and autonomy of the control system have opened the horizon to explore different assistive tasks in out-of-lab scenarios.