In this study, a mobile overground gait-training system (OGTS) was designed, and a prototype was manufactured to determine the feasibility and control stability of the designed system. Approval was received from the Institutional Review Board of Fu Jen Catholic University for conducting experimental testing on healthy individuals with the designed mobile OGTS. The designed system comprises a mobile electric walking aid (EWA), a body weight support system (BWSS), and an exoskeleton gait orthosis (EGO). The system can perform multiple functions for physical overground gait training. The mobile EWA and EGO can be operated separately from the mobile OGTS. An interval type-2 fuzzy sliding controller (IT2FSC) was designed to compensate for disturbances and uncertainties because the mobile OGTS has a coupling issue and potential subjects have different weights and body shapes. The mobile OGTS has one IT2FSC to provide a pulse-width modulation output to regulate two linear actuators for the BWSS, and it adopts four IT2FSCs to produce voltage outputs to control the gait trajectory of the EGO. Three experiments demonstrated that the mobile OGTS provides a stable control force to assist the user in overground gait training as well as assist-as-needed body weight support for gait training.