Magnesium ion conducting nanocomposite polymer electrolytes with different wt% of MgO nano-filler in optimum conducting composition of solid polymer electrolyte have been prepared by solution cast technique and characterized by various electrical and thermal techniques. The thermal stability in polymer electrolyte films was confirmed by Thermogravimetric analysis (TGA), reduction in melting temperature was confirmed by Differential scanning calorimetry (DSC) and decrease in degree of crystallnity was confirmed by X-Ray Diffraction (XRD). It was found that dispersion of nano-filer enhances ionic conductivity and dielectric constant, confirmed by complex impedance spectroscopy (CIS). The impedance spectroscopy technique performed in the frequency range between 42 Hz and 5 MHz at different temperatures and obtain highest conductivity 1.04 × 10−4 S/cm for optimum conducting composition (OCC) i.e. 70 PVDF:30 Mg(NO3)2:3MgO of NCPE thin film. The magnesium ion conduction in NCPE was confirmed by transference number measurement.