This study reports on the synthesis of cross‐linked networks of cardanol‐based polybenzoxazine (MCBZ) having pendant 2‐mercaptosuccinic acid with polyvinyl alcohol (PVA) to create hydrophilic polymer membranes. These membranes were further reinforced with varying weight percentages of zirconium oxide nanoparticles (ZrO 2 NPs) for proton transport membrane fuel cell (PEMFC) applications. The nanocomposites were characterized using FT‐IR, 1 H NMR, 13 C NMR, PXRD, FE‐SEM, and HR‐TEM analyses. Their physicochemical characteristics such as swelling ratio (SR), water uptake (WU), and ion‐exchange capacity (IEC) were systematically assessed. Among the prepared nanocomposite membranes, the membrane with 5 wt% ZrO 2 ‐dispersed PVA/MCBZ showed an optimal IEC of 1.5 meq g −1 and a proton conductivity of 1.096 × 10 −1 S/cm at 110°C. Arrhenius plots indicated low activation energies, suggesting efficient proton transport through the vehicular mechanism. The stability of membranes was estimated through Fenton's reagent testing at 80°C, which showed minimal chemical degradation. The ZrO 2 /PVA/MCBZ membrane demonstrated an improved maximum power density of 0.802 mW cm −2 at a current density of 2.26 mA cm −2 , surpassing the 0.530 mW cm −2 achieved by the PVA/MCBZ membrane at 1.19 mA cm −2 . Based on these results, the composite membranes show promising potential as membrane materials for fuel‐cell applications.