High efficient and environment friendly one-pot in situ microwave irradiation method was implemented towards the preparation of porous reduced graphene oxide/WO3 (rGOW) nanocomposites for the first time. Here, 3D porous WO3 nanoparticles were evenly decorated on 2D rGO sheets. The crystal phase purity and the functional group characterizations of the as-synthesized nanomaterials were examined by powder XRD and Raman spectral analyses. The morphological studies from the SEM, TEM, and BET measurements clearly revealed the highly porous nature of nano-sized WO3 and its distribution on the surface of rigid 2D graphene sheet. The UV along with visible light-driven degradation mechanism of malachite green (MG) dye in the rGOW nanocomposites was well illustrated with the schematic diagram and discussed in detail through the kinetics of the degradation process upon calculating the rate constant and half-life time. The rGO/WO3 photocatalyst delivered high MG degradation efficiency of 97% under UV irradiation.