Hydrogen is a clean‐energy fuel, but underground storage can be disrupted by native microbes that consume H₂ and build protective biofilms under high heat and pressure. We tested whether sulfate‐reducing Desulfovibrio could grow on hydrogen in Castlegate sandstone, a rock similar to a planned pilot site. In lab trials, crushed grains or blocks of sandstone were exposed to H₂, and we measured gas consumption and cell growth. After several weeks, H₂ levels fell by ~40% while cell counts tripled. Electron microscopy and nano–CT imaging revealed 2–10 µm thick, carbon‐rich biofilm layers coating quartz and feldspar grains. These results suggest sulfate reducers can colonize hydrogen reservoirs and may alter rock properties, insights that will inform future high-pressure, high-temperature tests and storage strategies.