5% Ru-doped MgO and PANI/MgO–Ru nanocomposite were successfully synthesized using sol–gel and in situ polymerization methods, respectively. Several characterization techniques were employed to analyze the structural, spectroscopic, topographical, elemental, and chemical properties of the synthesized materials using different characterization techniques. With the help of XRD patterns, the estimated crystallite sizes for 5% Ru-doped MgO nanoparticles and PANI/MgO–Ru nanocomposite were calculated to be 20 and 11 nm, respectively. By examining the SEM results, it was observed that all the materials possess a nearly spherical surface morphology. The availability of pores was also found at the surface of the materials which evinces that the synthesized materials can perform well in the context of gas sensing. The synthesized materials were also examined for LPG sensing investigations. Some noteworthy parameters of LPG sensing such as response time, recovery time, reproducibility, and sensitivity were estimated for all the materials. LPG sensing investigations reveal that the PANI/MgO–Ru might be a promising and excellent sensing material for the fabrication of an efficient LPG sensor.