A simple, cost-effective, ultrasound-assisted hydrothermal method was used to synthesize tungsten trioxide (WO₃) and subsequently a tungsten trioxide/reduced graphene oxide (WO₃/rGO) composite. The formation of the WO3/rGO composite was confirmed by XPS and Raman analyses. XPS analysis of the WO₃/rGO composite revealed the presence of tungsten, carbon, and oxygen. Raman spectroscopy confirmed the presence of G and D bands in the WO₃/rGO composite. The randomly arranged, interconnected, nanoplate-like morphology of WO₃ was destroyed owing to the presence of rGO nanosheets and converted into a highly porous nanostructure. Multifunctional WO₃ and WO₃/rGO photocatalysts were used to study the sonocatalytic degradation of hazardous Congo red (CR) azo dye and photocatalytic hydrogen production. The surface area of the WO₃/rGO composite (62.03 m²/g) was larger than that of WO3 (44.79 m²/g), thereby enhancing the efficiency of the sonocatalytic degradation and photocatalytic hydrogen production, which corresponds to the effective inter-charge transfer between WO3 and rGO. Platinum was used as a co-catalyst with WO₃/rGO to promote hydrogen production. The incorporation of rGO enhanced the CR dye degradation efficiency from 56 to 94% and the hydrogen production activity from 424.5 to 825.8 µmol/h·g.