Magnesium ion-conducting solid polymer electrolytes consisting of polyvinyl alcohol with magnesium perchlorate (Mg(ClO4)2) as electrolytic salt have been developed and their experimental investigations are reported. The solid polymer electrolytes have been prepared by well-known solution casting method using double-distilled water as a solvent. The highest room temperature conductivity of the order of 10−4 S cm−1 was obtained for the solid polymer electrolyte with the composition 80 mol% polyvinyl alcohol:20 mol% Mg(ClO4)2. The pattern of the temperature-dependent conductivity shows Arrhenius behavior. The Fourier transform infrared spectroscopy analysis confirms the complex formation of the polymer with the salt. The X-ray diffraction results reveal that the crystalline phase of polymer host has completely changed on the addition of dopant. Differential scanning calorimetry studies show a decrease in melting temperature of the polyvinyl alcohol with the increasing dopant concentration. The real part of dielectric permittivity shows a strong dispersion at lower frequencies, which implies the space charge effects arising from the electrodes. The loss tangent spectrum reveals that the jumping probability per unit time decreases with the increasing salt concentration. The total ionic transference number measured has been found to be in the range of 0.92–0.94 for all the polymer electrolyte systems. The result reveals that the conducting species are predominantly ions. The solid polymer electrolyte with highest conductivity showed an electrochemical stability of 2 V. The results obtained by cyclic voltammetry on stainless steel/solid polymer electrolyte/stainless steel, Mg/solid polymer electrolyte/Mg symmetrical cells show evidence for reversibility.