This study focuses on comprehensively investigating the crystal structure, electronic, magnetic and optical properties of pure and Pb-doped CdS at different concentrations using first-principles methods with the GGA-PBE+U approximation. Our calculations successfully reproduce the experimentally observed optimized lattice parameters and band gap values for both pure and Pb-doped CdS systems. Band structure results show a large and significant reduction in the band gap of Pb-doped CdS at low concentrations, followed by a steady increase at high Pb concentrations. The electron density distribution show the covalent nature between Cd-S and Pb-S. The optical properties of pur and Pb-doped CdS show: a significant increase in absorption and in reflectivity in the visible and ultraviolet domains with doping. Finally, a reduction in optical transmission in the visible energy domain. These optical analyzes provide essential information on the behavior of these materials, thus broadening its practical applications, notably in the design of optoelectronic devices.