The synthesis and design of low-cost visible-light-active catalysts for the photodegradation of organic dyes have been regarded as an efficient way to use solar energy in addressing environmental issues. We report the fabrication of MoS₂/CdS nanoparticles functionalized with Bi₂S₃ nanoflakes. The ternary composites of “MoS₂/CdS/Bi₂S₃” were synthesized in situ by a hydrothermal method at different temperatures. The changes in structural, optical, and morphological properties of the synthesized CdS/MoS₂/Bi₂S₃ were explored. The effects of Bi₂S₃ on CdS/MoS₂ were thoroughly studied by performing an X-ray diffractometer (XRD), a scanning electron microscope (SEM), an ultra-violet–visible spectrometer (Uv–vis), and Fourier transform infrared spectroscopic (FT-IR) studies of the nanoparticles. XRD confirms the cubical crystal structure of the nanoparticles. SEM studies possess the modulation in the surface morphology with the tenability in volume ratios of “MoS₂/CdS/Bi₂S₃” composites. It was observed that the bandgaps calculated using absorption measurements could be manipulated from 2.40 eV to 0.97 eV with varying Bi₂S₃ in the MoS₂/CdS nanostructures. FT-IR confirmed the synthesis of “MoS₂/CdS/Bi₂S₃” nanoparticles. On allowing the visible light to fall for 120 min, it was observed that “MoS₂/CdS/Bi₂S₃” degrades the methylene blue up to 90%. The calculated results of “MoS₂/CdS/Bi₂S₃” suggest that the synthesized material could be a strong candidate for photodegradation applications. This research work explains the synthesis of MoS₂/CdS/Bi₂S₃-based nanocomposites for the degradation of dye using a photocatalytic process. The final results show that this catalyst effectively degrades the dye.