Nanomaterials integrated surface acoustic wave (SAW) gas sensing technology has emerged as a promising candidate for real-time toxic gas sensing applications for environmental and human health safety. However, the development of novel chemical interface based on two-dimensional (2D) sensing materials for SAW sensors for the rapid and sensitive detection of NH₃ gas at room temperature (RT) still remains challenging. Herein, we report a highly selective RT NH₃ gas sensor based on sulfur-doped graphitic carbon nitride quantum dots (S@g-C₃N₄ QD) coated langasite (LGS) SAW sensor with enhanced sensitivity and recovery rate under ultraviolet (UV) illumination. Fascinatingly, the sensitivity of the S@g-C₃N₄ QD/LGS SAW sensor to NH₃ (500 ppb) at RT is dramatically enhanced by ~ 4.5-fold with a low detection limit (~ 85 ppb), high selectivity, excellent reproducibility, and fast response/recovery time (70 s/79 s) under UV activation (365 nm) as compared to dark condition. Additionally, the proposed sensor exhibited augmented NH₃ detection capability across the broad range of relative humidity (20%–80%). Such remarkable gas sensing performances of the as-prepared sensor to NH₃ are attributed to the high surface area, enhanced functional groups, sulfur defects, UV photogenerated charge carriers, and facile charge transfer in the S@g-C₃N₄ QD sensing layer, which further helps to improve the gas molecules adsorption that causes the increase in conductivity, resulting in larger frequency responses. The gas sensing mechanism of S@g-C₃N₄ QD/LGS SAW sensor is ascribed to the enhanced electroacoustic effect, which is supported by the correlation of resistive type and COMSOL Multiphysics simulation studies. We envisage that the present work paves a promising strategy to develop the next generation 2D g-C₃N₄ based high responsive RT SAW gas sensors.