With the combination of experimental and computational approaches, the impact of hydrogenation on the optical, electronic and electrochemical properties of Fe2O3 for water splitting have been studied. Under high pressure, hydrogen incorporation into the Fe2O3 lattice has been achieved, and hydrogen dopants can be released with heat treatment. With H-doping, magnetite Fe3O4 has been found to form at the edge of Fe2O3 nanoparticles. H-incorporation can narrow the band gap by ∼0.4 eV and slightly reduce the overpotential (by 140 mV) for oxygen evolution reaction, but due to the localization of hydrogen (bonded with oxygen), a slightly lower charge carrier density resulted. Computational studies reveal that all of the above changes are essentially related to the local states brought by H-dopants. This study provides an in-depth understanding of the optical, electronic, and catalytic properties of hydrogenated Fe2O3.