Thiourea base ligands and their corresponding metal complexes were prepared and used as precursors to grow the ZnS thin films onto the glass substrates by thermal decomposition of the substituted thiourea zinc complexes. The deposited ZnS thin films were annealed at 300, 400, and 500 °C for an hour, respectively. The structural and optical properties of the prepared ligand, zinc complexes and deposited films were achieved through FTIR, TGA, UV–Vis, PL, XRD, and SEM. FTIR spectra of the complexes exhibited the peaks between 470 and 450 cm−1 that correspond to the bond between the zinc and sulphur. The optical properties of the prepared thin films were established at the wavelength ranging from 200 to 800 nm. The bandgaps of all the prepared ZnS thin films were found to be in the range of 2.71–3.56 eV. X-ray diffraction patterns of all the synthesized thin films mainly exhibited cubic phase structures. SEM images showed uniform structured particles of the films that were grown at higher temperature.