A novel aminopropyl functional group bearing magnesium phyllosilicate clay (AC)/Nafion nanocomposite films with embedded platinum nanoparticles (Pt/AC/N) was prepared by sol-gel method followed by solution casting for various compositions of AC in Nafion. The as prepared nanocomposite films were subjected to surface characterization by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The thermal and mechanical stabilities were analyzed by thermogravimetric analysis (TGA) and nanoindentation coupled scanning probe microscopy analysis (SPM). The protonic conductivity of AC/Nafion nanocomposite films with and without Pt nanoparticles was measured by electrochemical impedance spectroscopy (EIS) using a two-probe conductivity cell. It was found that 6wt.% AC/Nafion possesses a high proton conductivity of 1.38×10-4Scm-1, a thermal stability of up to 360°C (60°C higher than pristine Nafion) and a high mechanical stability (78.76MPa) among the different compositions studied. The catalytic activity of the optimized nanocomposite film containing Pt nanoparticles (Pt/6wt.% AC/N) towards oxygen reduction reaction (ORR) was investigated by cyclic voltammetry (CV) and linear scan voltammetry (LSV) techniques under hydrodynamic conditions. It was observed that 35.4μgcm-2 Pt/6wt.% AC/N composite film has higher ORR limiting current density of 4.2mAcm-2, and also it is interesting to note that this composition exhibited a high conductivity of 1.75×10-3Scm-1 indicating that the nanocomposite catalyst film could be used as a proton conductor as well as a catalyst layer for the fabrication of membrane electrode assemblies in PEM fuel cells.