CdS nanoparticles (CdS NPs) and CdS nanoslabs (CdS NSs) were synthesized from the single source (SS) and multi-source (MS) precursors, respectively. Our target was to observe any change in morphology by altering the synthetic route. CdS NPs with spherical morphology (0.2–0.5 µm in diameter) were obtained by using the SS precursor route via the formation of a Cd-complex. CdS NSs (100–200 nm in length, 50–100 nm wide and 25–50 nm in thickness) were obtained by using the MS precursors, by direct addition of the ligand to metal salt. Both NPs and NSs were used for the degradation of four different cationic organic dyes viz., malachite green (MG), methylene blue (MB), rhodamine B (RhB) and methyl violet (MV) under visible light. CdS NPs synthesized from SS precursor exhibited higher photocatalytic activity than CdS NSs fabricated via MS precursor due to spherical morphologies (small size of particles increases the surface area) and higher band gap. On the other hand, CdS NSs show sheet or cube like morphologies. The kinetic study proved that the rate constants for the MG, MB, MV, and RhB degradation by CdS NPs (1.65 × 10^–2, 1.25 × 10^–2, 1.2 × 10^–2, and 1.24 × 10^–2 min^–1, respectively) are higher than those for CdS NSs (1.45 × 10^–2, 1.13 × 10^–2, 1.05 × 10^–2, 1.14 × 10^–2 min^–1, respectively). The precursors were characterized by ¹H and ¹³C nuclear magnetic resonance. Phase pattern and composition of CdS were confirmed by X-ray diffraction and energy dispersive X-ray spectroscopy. Morphology and size were confirmed by transmission electron microscopy and scanning electron microscopy.