Herein, the full potential linearized augmented plane wave (FP‐LAPW) method based on density functional theory has been used to compute the electro‐optical and magnetic characteristics of Mg1−xNixS (x = 0%, 6.25%, 12.5%, and 25%) alloys. The stability of the Mg1−xNixS alloys is verified by the enthalpy of formation energy. In electronic features, the band structure and density of states (DOS) demonstrate the semiconducting behavior in pristine MgS compound, while Mg1−xNixS alloys show half‐metallic ferromagnetic to metallic behavior based on the doping concentration. DOS exhibit a strong pd‐hybridization between Ni‐d and S‐p orbitals in the conduction band). For 6.25%, 12.5%, and 25% concentrations, the calculated total magnetic moment is 1.45364, 1.93086, and 0.71829 μB, respectively which is primarily owing to transition metal d states. Optical characteristics including refraction, absorption, complex dielectric function, and reflectivity are studied in the range of 0–10 eV at various concentrations. The absorption of light is noted from visible to UV spans which increase their significance for optoelectronic usages. Results of Mg1−xNixS alloys reveal their potential applications in optical and magnetic storage devices.