Crystal surfaces play significant role in controlling the photocatalytic properties of a semiconductor material. In this work, we report the controlled synthesis of various BiFeO₃ nanostructures and validate the influence of various crystal surfaces towards photocatalytic properties for water oxidation. The synthesis of BiFeO₃ nanostructures including hexagons, rectangular cuboids and nanoplates is achieved in NaOH aqueous solutions with various concentrations via a facile hydrothermal method. High-resolution transmission electron microscopy (HRTEM) revealed NaOH concentration dependent growth direction of various BiFeO₃ nanostructures. BiFeO₃ rectangular cuboids dominated with (102) crystal facets exhibited higher surface photovoltage (SPV) response confirming efficient charge carrier separation compared to hexagons and nanoplates. Furthermore, the photoelectrochemical measurements also confirmed the improved photocurrent density and positive shift in flat band potential for BiFeO₃ rectangular cuboids studied via Mott-Schottky plots. Resultantly, BiFeO₃ rectangular cuboids demonstrated superior photocatalytic O₂ evolution activity of 82.2 µmol h⁻¹ g⁻¹ compared to 42.6 µmol h⁻¹ g⁻¹ and 53 µmol h⁻¹ g⁻¹ for hexagons and nanoplates, respectively, without any cocatalyst under visible light irradiation.