In the conventional sliding mode control (SMC), the four-leg distribution static compensator (DSTATCOM) currents are controlled based on a current error in each phase. However, the four currents in a four-wire system cannot be independently controlled variables and hence one of the four controllers is redundant in the conventional schemes. Further, the current dynamics of a DSTATCOM converter are coupled through converter pole voltages in the natural frame. This leads to cross-coupling in the sliding variable dynamics with respect to four manipulated input variables, thereby the design of conventional SMC makes difficulty in selecting the control input according to Lyapunov stability criteria. To eliminate this coupling, the new sliding surface function is structured considering the current due to Thevenin's equivalent load neutral-point voltage as a fourth independent controlled variable. The performance of a DSTATCOM with the proposed control scheme under various operating conditions is validated through a detailed simulation study and experimental results obtained from a laboratory prototype of four-leg DSTATCOM.