Cu$_2$ZnSnS$_4$ (CZTS) thin films for three samples were prepared at the same deposition parameters by thermal evaporation method at a vacuum pressure of 6.0×10$^{−5}$ Torr and investigated using irradiation technique. The films deposited were irradiated with the gamma irradiation source (Cs-137) when activity = 1317.72 MBq, dose rate = 100.686 Gy/h for 300 and 600 Gy doses to study the influence of gamma irradiation on the structural, morphological and optical properties of the films. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and UV–V is were used to investigate the properties of the as-deposited and irradiated films. X-ray diffraction (XRD) studies of the as-deposited and irradiated thin films revealed a kesterite structure with tetragonal lattices at a preferred orientation along 2θ = 28.55◦. The intensity of the preferred peaks and the crystallite sizes showed a significant decrease with an increase in irradiation dose. Other microstructural parameters such as microstrain, dislocation density and the texture coefficient increase with the increase in irradiation dose. The field emission scanning electron microscopy (FESEM) images from the surface morphology investigation indicated that the as-deposited thin film was non-uniform and irradiated films became more compact and uniform with distinct grain size as the gamma radiation dose increases. Optical properties including band gap, absorption coefficient, transmittance and absorbance spectra for both as-deposited and irradiation films were also studied. It was found that the band gap for the as-deposited, 300 Gy and 600 Gy films were 1.48, 1.50 and 1.53 eV respectively. The absorption coefficient (α) decreased from 7.1235 to 5.6056×10$^4$ cm$^{−1}$. The influence of irradiation dose used in this work has shown a positive influence on the structural, morphological and optical properties.