In this work, Cu(I) oxide –decorated Polypyrrole nanocomposite (PPy-Cu₂O) was synthesized by in-situ polymerization, and a high- performance NH₃ gas sensing activity was studied along with regioselective synthesis of 1,4-disubstituted-1,2,3- triazoles and 2- (Phenyl)-quinazolin-4(3H)-ones. Cu₂O nanoparticles were synthesized via a green synthesis approach employing Ocimum tenuiflorum leaf extract as a biogenic reducing agent and CuCl₂·2H₂O as the copper precursor. The morphology, composition and chemical state and morphology of the PPy-Cu₂O nanocomposite was characterized by XRD, FTIR, SEM-EDX, TEM and XPS. The UV–Vis optical band gaps of PPy, Cu₂O, and the PPy–Cu₂O nanocomposite were determined to be 3.1 eV, 3.0 eV, and 2.9 eV, respectively. Notably, the PPy–Cu₂O nanocomposite exhibited enhanced NH₃ gas sensing performance, achieving a maximum sensitivity of 52.9% at 500 ppm, compared to 17.3% for pristine PPy. Response times for the nanocomposite at 100, 300, and 500 ppm NH₃ concentrations were 85 s, 70 s, and 60 s, respectively, with corresponding recovery times of 100 s, 120 s, and 135 s. In addition to its sensing capability, PPy–Cu₂O demonstrated catalytic efficiency in the regioselective synthesis of 1,4-disubstituted-1,2,3-triazoles in aqueous medium at room temperature, using both terminal and internal alkynes—without the need for any base, ligand, or reducing agent. Furthermore, the nanocomposite was successfully employed in the synthesis of 2-phenylquinazolin-4(3H)-ones via the condensation of anthranilamide (1 mmol) and 4-methylbenzaldehyde (1.2 mmol) under varied reaction conditions. This work introduces a novel, multifunctional nanocatalyst that offers cost-effective and high-performance NH₃ sensing alongside green synthetic protocols for value-added heterocycles. The study underscores the potential of PPy–Cu₂O as a sustainable platform for both sensing and catalytic applications, demonstrating strong potential for environmental and pharmaceutical applications.