Reduced graphene oxide (RGO)-supported bismuth ferrite (BiFeO3) (RGO-BFO) nanocomposite is synthesized via a two-step chemical route for photoelectrochemical (PEC) water splitting and photocatalytic dye degradation. The detailed structural analysis, chemical coupling, and morphology of BFO- and RGO-supported BFO are established through X-ray diffraction, Raman and X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy studies. The modified band structure in RGO-BFO is obtained from the UV-vis spectroscopy study and supported by density functional theory (DFT). The photocatalytic degradation of Rhodamine B dye achieved under 120 min visible-light illumination is 94% by the RGO-BFO composite with a degradation rate of 1.86 × 10-2 min-1, which is 3.8 times faster than the BFO nanoparticles. The chemical oxygen demand (COD) study further confirmed the mineralization of an organic dye in presence of the RGO-BFO catalyst. The RGO-BFO composite shows excellent PEC performance toward water splitting, with a photocurrent density of 10.2 mA·cm-2, a solar-to-hydrogen conversion efficiency of 3.3%, and a hole injection efficiency of 98% at 1 V (vs Ag/AgCl). The enhanced catalytic activity of RGO-BFO is explained on the basis of the modified band structure and chemical coupling between BFO and RGO, leading to the fast charge transport through the interfacial layers, hindering the recombination of the photogenerated electron-hole pair and ensuring the availability of free charge carriers to assist the catalytic activity.