Tractor semi-trailers are increasingly playing an important role in freight transportation worldwide. Although most tractor semi-trailers are equipped with a passive anti-roll bar system, however accidents involving this type of vehicle are still frequent and have serious consequences. This paper presents an H∞ controller design for an active anti-roll bar system in order to enhance the roll stability of a tractor semi-trailer with the torque control generated at all axles. The considered performance outputs include the lateral acceleration, the normalised load transfer for both tractor and semi-trailer, as well as the magnitude of the torque control to avoid the actuator’s saturation. The effectiveness of the proposed method is evaluated in the frequency domain via the transfer function magnitude from the steering angle to the survey signals, and in the time domain through the nonlinear vehicle model of TruckSim ® software. The evaluation results show that the roll stability of the tractor semi-trailer using the H∞ active anti-roll bar system has improved by more than 20% compared to a passive vehicle.