Before and after irradiation, the impact of gamma rays on the structure, optical, electrical, and DFT of SnNC thin films preserved by thermal evaporation were investigated. The SnNC compound’s noteworthy band gap of 0.932 eV is in good agreement with the indirect optical band gap observed in experiment. The optical band transitions exhibit an increase with the γ-irradiation dose of 50 kGy, from 0.99 eV to 1.50 eV for the as-prepared SnNC thin films to 1.18 eV and 1.83 eV. The location and intensity fluctuations of the real sections of the refractive index (n) for SnNC thin films exposed to γ-rays at varying doses are shown. The photoluminescence spectrum’s peak emission at 675 nm (1.84 eV) is ascribed to the band-to-band transition, and this value is in good agreement with the estimated value of EgTauc. For SnNC thin films as-prepared, the dc electrical activation energy values are ΔE = 0.55 eV, and for both heating and cooling operations, they are 0.28 eV and 0.46 eV at 50 kGy γ-irradiation dose. The impact of varying doses of γ-ray irradiation on the optical parameter values indicates that SnNC thin films have potential uses in optoelectronic or dosimeter devices.