Mechanically stable, proton-conducting, and very cost-effective nanocomposite membrane was synthesized successfully using a simple and scalable phase-inversion approach. Phosphotungstic acid (PWA) and zirconium phosphate (ZRP) were synthesized using sol–gel and co-precipitation method, respectively. PWA-ZrP nanoparticles showed remarkable compatibility with cross-linked poly(vinyl alcohol) (c-PVA) and thus forming uniform and defect-free composite membrane of thickness ∼100–120µm. Doped PWA-ZRP nanoparticles into c-PVA membrane led to introduced bronsted acidic sites, and thereby, drastic improvement in proton conductivity of membrane was observed. Composite membrane revealed excellent water-holding capabilities with proton conductivity of 5.2 × 10−5 Scm−1 under fully hydrated conditions (i.e., 98% relative humidity). The synthesized proton-conducting nanocomposite membrane was demonstrated as a potential advanced functional solid electrolyte for possible application in proton exchange membrane fuel cell.