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Herein, a simple, economical and low temperature synthesis of leaf-shaped CuO nanosheets is reported. As-synthesized CuO was examined through different techniques including field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), fourier transform infrared spectroscopic (FTIR) and Raman spectroscopy to ascertain the purity, crystal phase, morphology, vibrational, optical and diffraction features. FESEM and TEM images revealed a thin leaf-like morphology for CuO nanosheets. An interplanar distance of ~0.25 nm corresponding to the (110) diffraction plane of the monoclinic phase of the CuO was revealed from the HRTEM images XRD analysis indicated a monoclinic tenorite crystalline phase of the synthesized CuO nanosheets. The average crystallite size for leaf-shaped CuO nanosheets was found to be 14.28 nm. Furthermore, a chemo-resistive-type gas sensor based on leaf-shaped CuO nanosheets was fabricated to effectively and selectively detect H₂S gas. The fabricated sensor showed maximum gas response at an optimized temperature of 300 °C towards 200 ppm H₂S gas. The corresponding response and recovery times were 97 s and 100 s, respectively. The leaf-shaped CuO nanosheets-based gas sensor also exhibited excellent selectivity towards H₂S gas as compared to other analyte gases including NH₃, CH₃OH, CH₃CH₂OH, CO and H₂. Finally, we have proposed a gas sensing mechanism based upon the formation of chemo-resistive CuO nanosheets.