This paper presents a cost-function based predictive voltage control strategy with a prediction horizon of two samples to effectively control the output voltage of three-phase four-leg inverter used for the standalone power systems. The three-phase inverter with an additional leg is developed to deliver symmetrical sinusoidal three-phase voltages irrespective of the arbitrary consumer load profiles. The proposed controller uses the discrete model of the inverter and RLC filter for two-step prediction of output voltage for each switching state of the inverter. The control method chooses a switching state that minimizes the error between the output voltage and its reference. The proposed controller offers an excellent reference tracking with less voltage harmonic distortion for balanced, unbalanced and nonlinear loading conditions. The feasibility of the proposed control scheme has been verified by MATLAB/Simulink.