Motivated by fundamental interest and practical applications, the investigations of two-dimensional photocatalysts are fascinating subjects in clean energy. Herein, we propose that two-dimensional Li-based ternary chalcogenides LiXY2 (X = Al, Ga, In; Y = S, Se, Te) have intrinsic polarization and direct band gaps. Our results show that LiXY2 materials possess optical absorption spectra covering the visible and ultraviolet range. We show that these materials possess extremely high electron mobility (∼103 cm2 V-1 s-1), providing great potential in overall water splitting. Furthermore, LiAlS2 and LiGaS2 can facilitate overall water splitting regardless of their energy gaps because of the large differences of surface electronic potentials of LiXY2. Importantly, it is feasible to exfoliate the layered LiAlTe2 from its bulk counterpart in experiments. Our findings open an exotic pathway to realizing promising photocatalytic applications in two-dimensional ternary materials.