Limited light absorption, inefficient electron-hole separation, and unsuitable positions of conduction band bottom and/or valence band top are three major critical issues associated with high-efficiency photocatalytic water treatment. The addition of reduced graphene oxide (rGO) is one of the key strategies to address the above-mentioned issues. In this research, novel bismuth oxyiodides flower-like Bi4O5I2 and Bi5O7I were incorporated on rGO by a simple ultrasound-assisted room temperature approach. The crystal structure, morphology, optical properties, surface area, and the photocurrent of the prepared composites were investigated systematically by various analytical techniques. The chemical oxidation state of the elements present in the catalyst was ascertained by X-ray photoelectron spectroscopy spectra. The effect of ultrasound-assisted room temperature synthesis not only improved the crystallinity of Bi4O5I2 and Bi5O7I but also increased the surface area and loading of Bi4O5I2 and Bi5O7I on rGO sheets. The photocatalytic activity of the prepared catalyst was evaluated via photocatalytic degradation of methyl orange pollutant under the visible light illumination. A maximum photocatalytic dye degradation rate of 98% in 30 min under visible light irradiation was achieved for Bi5O7I coupled with 8 wt % of rGO which was beneficial to enhance separate photogenerated electron-hole pairs. In addition, a study of extended reusability showed that the prepared catalyst could be used effectively for five cycles without an apparent deactivation of the photocatalytic activity. A possible mechanism of Bi5O7I/rGO composites as photocatalysts has been proposed.