Driven by a curiosity of how sulfur (S) alters the physical properties of KTaO3, we embarked on a computational journey using the WIEN2k code and the insights of density functional theory (DFT). We aim to unravel the influence of S-substitution on the material's structure, electronic behavior, optical responses, mechanical strength, and thermodynamic characteristics of KTaO3. Our investigation has unveiled a remarkable structural transformation, wherein the cubic phase of KTaO3 undergoes a shift to a tetragonal configuration for KTaO2S and KTaOS2, eventually returning to a cubic phase in KTaS3. Significantly, the band gap values have undergone substantial alterations, presenting energy gaps of 1.808 eV, 0.264 eV, and 0.078 eV for KTaO2S, KTaOS2, and KTaS3, respectively, diverging from the original band gap of 3.572 eV in KTaO3. Importantly, all these compounds have exhibited mechanical and dynamical stability. Furthermore, these compounds have displayed promising optical features characterized by high absorption coefficients (∼105 cm−1), minimal reflectivity (<30%), and robust optical conductivity within the visible spectrum, making them ideal candidates for a range of optoelectronic technologies. Our comprehensive investigation has reinforced the stability of all computed phases, showcasing exceptional electronic, optical, and thermo-mechanical properties, including semiconducting behavior, hardness, ductility, anisotropy, high absorptivity, and low reflectivity. The modified band gap and optical characteristics of KTaO2S indicate considerable potential for its application in solar cells, presenting promising opportunities to improve solar energy conversion efficiency. The thermal conductivity of KTaO3 is fascinating and shows substantial promise for applications as a heat sink material.