Nonstoichiometric Y2Ti2O7 pyrochlores with Ti/Y ratios ranging from 0.95 to 1.15 were prepared by an aqueous sol–gel method and annealed at different temperatures. These synthesized catalysts were characterized by X-ray diffraction, UV/Vis reflectance spectroscopy, and electron microscopy. The samples were loaded with nanoparticles of rhodium or platinum acting as co-catalysts and tested for photocatalytic hydrogen production in the presence of methanol as sacrificial agent. It was found that the cationic lattice distortion in the Y2Ti2O7 structure is significantly influenced by the Ti/Y ratio and the annealing temperature. By optimization of these parameters, the intrinsic cationic distortion characterized by yttrium and titanium interchanging their lattice positions was minimized. Probing the materials in the hydrogen production test reaction revealed that the photocatalytic activity of pyrochlore mixed oxides is clearly determined by the cationic lattice distortion and can be tuned considerably.