Sulfonated poly(arylene ether sulfone) with degree of sulfonation of 50 mol.% (SPAES50) was synthesized for the preparation of a hydrocarbon-based membrane and ionomer, for application to proton-exchange membrane water electrolysis (PEMWE) as an alternative to Nafion™. The SPAES50 membrane showing the excellent physical and electrochemical properties as well as the SPAES50-based ionomer (P50) were prepared and applied to PEMWE to evaluate its performance. The effects of the membrane thickness and ionomer content were also investigated to realize high-performance SPAES-based PEMWE. The proposed SPAES-based PEMWE showed higher performance than that of commercial PEMWE with a Nafion™ membrane and ionomer. Additionally, this is the best performance reported to date, and it is attributed to the low ohmic resistance caused by the high proton conductivity of SPAES50 membrane and the small membrane thickness (20 μm). Therefore, we demonstrate the great potential of SPAES50 as a hydrocarbon-based membrane and ionomer in PEMWE.