Indium sulfide, a two-dimensional semiconductor material, has emerged as a promising candidate for costeffective and sustainable solar cells. This report deals with the facile preparation of colloidal In₂S₃ with a new ultrathin nanosheet (NS) morphology. The synthesis was mediated through a new structurally characterized single source molecular precursor. The crystal structure, phase purity, and morphology of the NSs were thoroughly investigated by pXRD, Raman, XPS, and electron microscopic techniques. AFM studies revealed that the NSs have an average thickness of ~1.76 nm. The optical studies confirm quantum confinement in the as-prepared NSs with a blue shift in the direct band gap, which lies in the optimal range suitable for solar cell application. Furthermore, photoluminescence studies indicate strong emission by these NSs in the blue region. The as-synthesized In₂S₃ NSs-based prototype photoelectrochemical cell exhibit high photostability and photoresponsivity, which make them suitable candidates for sustainable solar cells.