Poly(styrene sulfonic acid) (PSSA) content in poly(vinyl alcohol) (PVA) and PSSA blend membrane is varied and its effect on proton conductivity is studied at varying relative humidity (RH) values. The maximum proton conductivity is observed for the PVA–PSSA membrane with about 35 wt. % PSSA at all humidity values. At 30% RH value, the conductivity of PVA–PSSA blend membrane is $1.20 \times 10^{-3} S/cm$, which is about two orders of magnitude higher than the conductivity value of $2.27 \times 10^{-5} S/cm$ observed for pristine PVA membrane. Water self-diffusion coefficients and water release kinetics of these materials have been characterized by nuclear magnetic resonance (NMR) imaging technique, which validate the use of this membrane in polymer electrolyte fuel cells (PEFCs). A peak power density of $210 mW/cm^2$ at a load current-density of $500 mA/cm^2$ is achieved for the PEFC with the optimized PVA–PSSA membrane as electrolyte compared to a peak power density of only $38 mW/cm^2$ observed at a load current-density of $80 mA/cm^2$ for the PEFC with pristine PVA membrane as electrolyte while operating at 75 °C with $H_2$ and $O_2$ feeds to the fuel cell maintained at atmospheric pressure.