A solid polymer electrolyte (SPE) film with improved mechanical and thermal stability has drawn significant attention in the field of polymer research due to their technological applications in energy storage devices. We have explored the electrical properties of the blend SPE composed of 20 wt.% poly(ethylene oxide), 80 wt.% polyvinylidene fluoride, and 35 wt.% NH4I by introducing a plasticizer ethylene carbonate (EC). A significant enhancement of electrical conductivity has been found in the composite SPE containing 80 wt.% of EC. We have confirmed the formation of a hydrogen bonding network between the carbonyl group (C=O) of EC and the cations NH+4 . Therefore, EC facilitates the new coordination sites via the hydrogen bonding network with the cations NH+4 , which eventually leads to the enhancement of conductivity up to a maximum value of 1.2 × 10−4 S/cm at 80 wt.% of EC. The increase in the relative percentage of contact ions over free ions at 80% of EC, as estimated from the FTIR study, is thus intriguing. Therefore, we have proposed an ion transport mechanism based on ion hopping through different coordinating sites mediated by EC. Dielectric relaxation of the composite SPE has been best delineated by a two-parameter Mittag-Leffler function. The exponents obtained from the fit of the experimental decay function with the two-parameter Mittag-Leffler function in the entire time domain are positive and less than one, suggesting non-Debye relaxation in the polymer composite system under investigation.