Among various prevalent and dangerous air pollutants, nitrogen dioxide (NO2) is one of them, which causes climate change and degradation of air quality. Consequently, there is a high demand for inexpensive, dependable, and sensitive devices to detect NO2 gas. Among various available materials carbon nanotubes (CNTs) shows excellent electronic properties and a very good porous material which enhance the sensitivity of the sensor drastically. Thus, in the present work efforts have been made to develop gas sensors for efficient detection of NO2 gas. CNT/CdS/SnO2 based ternary nanocomposites have been prepared via chemical route and thin film of CNT/CdS/SnO2 nanocomposite was deposited using drop cast method onto an interdigitated electrodes (IDE) for the fabrication of conductometric gas sensor for the detection of NO2 gas at trace level. To study the structural and optical properties of the developed sensor X-ray diffraction (XRD) and UV-Visible spectroscopy were performed. Interestingly, when CNT was added to the CdS/SnO2 nanocomposite, the sensor showed more prominent gas sensing properties compared to that obtained for the CdS/SnO2 nanocomposite-based sensor. The sensing response of the prepared CNT/CdS/SnO2 nanocomposite-based sensor was studied toward 1 ppm concentration of the NO2 gas. Incorporation of CNT in CdS-SnO2 nanocomposite yielded a maximum sensing response of 1.9 × 102 with a very fast response time of 4 s and recovery time of 22 s toward 1 ppm concentration of the target gas at operating temperature 70 °C. The limit of detection (LOD) for the prepared sensor was found to be 50 ppb.