Studies on magnesium ion conducting blend polymer electrolyte (BPE) at room temperature are reported. BPE films of optimized 92.5PVA:7.5PAN ratio in view of its maximum conductivity with various concentrations of magnesium salt—Mg(NO3)2—of different molar mass percentages (0.1, 0.2, 0.3, and 0.4 m.m.%) have been prepared using solution-casting technique with dimethylformamide (DMF) as solvent. The promising characteristic features of these films have been studied. Possible conformational changes in the polymer host 92.5PVA:7.5PAN due to Mg(NO3)2 entrapment have been investigated by FTIR and XRD analysis. The composition 92.5PVA:7.5PAN:0.3 m.m.% Mg(NO3)2 offers maximum electrical conductivity of 1.71 × 10−3 S/cm at room temperature. The σ values follow the Arrhenius equation, and the activation energy for the optimized composition is 0.36 eV. The variations in glass transition temperature have been found using differential scanning calorimeter. Mg2+ ion conduction in the BPE film is confirmed using transference number measurement and cyclic voltammetry. The transport number of the Mg2+ ion is 0.30. Using linear sweep voltammetry, the electrochemical stability window for the highest BPE has been measured. Primary magnesium battery has been constructed using the maximum conducting membrane, and its output characteristics have been studied