Solid electrolyte for electrochemical device applications have been developed using a linear anionic polysaccharide, Gellan gum incorporated with Ammonium formate (NH₄HCO₂) by the solution casting technique using double distilled water as solvent. The amorphous nature and the crystallinity percentage of the polymer membranes have been calculated from X-ray Diffraction (XRD) technique and the complex formation between the polymer and salt have been studied using Fourier transform infrared (FTIR) technique. Ionic conductivity of developed membranes has been found by measuring its impedance. Polymer membrane (1 g Gellan gum: 0.9 M.wt % of NH₄HCO₂) exhibits the conductivity of 5.62 ± 0.09 × 10^–3 S/cm. The Differential Scanning Calorimetric (DSC) thermograms have been used to study the glass transition temperature in the membranes. The predominant transportation of ions has been proved by DC Wagner’s Polarization technique. The electrochemical stability for the highest ion conducting polymer membrane has been studied using Linear sweep Voltametry (LSV). Using highest conducting polymer membrane as an electrolyte, the electrochemical devices – primary battery, rechargeable battery and proton exchange membrane (PEM) fuel cell have been constructed and their performance has been analyzed. The primary battery exhibited the open circuit voltage (OCV) of 1.78 V, the rechargeable battery provided the highest potential of 2.27 V and the PEM fuel cell exhibits the OCV of 763 mV.