We report the fabrication of 2D ZnIn2S4 nanosheet/1D TiO2 nanorod heterojunction arrays by a facile hydrothermal process and their use as photoelectrodes in a photoelectrochemical (PEC) cell for high-performance solar water splitting. The morphology, microstructure, and phase of pristine TiO2 and 2D ZnIn2S4 nanosheet/1D TiO2 nanorod heterojunction arrays were characterized in detail. PEC measurements showed that 2D/1D heterojunction arrays offered enhanced photocurrent density (3 times higher than that of pristine TiO2), negatively shifted onset potential from 0.05 to −0.53 V, and high light on/off cycle stability. Electrochemical impedance investigation attested to a significant improvement of the interface electron transfer kinetics in this heterojunction, thus facilitating electron–hole separation, transfer, and collection, which resulted in enhanced PEC properties.