Nanocrystalline materials have garnered significant recognition in the scientific and research community for developing X-ray sensors. The applicability of bismuth-based binary and ternary compounds has been extensively studied in X-ray imaging and cancer therapy applications owing to their high attenuation. Among the binary and ternary compounds of bismuth, the n-type semiconductor silver bismuth sulfide (AgBiS2) was studied for the detection of X-rays at lower doses, based on its total attenuation (μ = 3.07 cm2 g−1 at 70 keV), density (ρ = 7.02 g cm−3), and bandgap (Eg = 1.21 eV). The effect of grain size on X-ray sensing performance was examined to validate the effective size required for maximum attenuation of X-rays and successful extraction of induced mobility carriers. X-ray sensors with four different AgBiS2 grain sizes were cast on interdigitated electrodes (IDEs) and subjected to different doses of X-rays at 2 V bias to study its dose-dependent X-ray sensing nature using an intra-oral (70 kVp-AC) X-ray machine. AgBiS2-based X-ray sensor exhibited the highest sensitivity of 20.13 μC mGy−1 cm−3 with the lowest Noise-equivalent dose ratio (NED) of 0.08 μGy Hz−0.5, 0.20 mGy detection limit and a response time of 0.12 s. This outcome validates that AgBiS2 can be applied as a potential replacement for perovskites in direct X-ray detection.