The solar-driven splitting of hydrohalic acids (HX) is an important and fast growing research direction for H 2 production. In addition to the hydrogen, the resulting chemicals (X 2/X 3−) can be used to propagate a continuous process in a closed cycle and are themselves useful products. Here we present a strategy for photocatalytic hydrogen iodide (HI) splitting using methylammonium lead iodide (MAPbI 3) in an effort to develop a cost-effective and easily scalable process. Considering that MAPbI 3 is a water-soluble ionic compound, we exploit the dynamic equilibrium of the dissolution and precipitation of MAPbI 3 in saturated aqueous solutions. The I− and H+ concentrations of the aqueous solution are determined to be the critical parameters for the stabilization of the tetragonal MAPbI 3 phase. Stable and efficient H 2 production under visible light irradiation was demonstrated. The solar HI splitting efficiency of MAPbI 3 was 0.81% when using Pt as a cocatalyst.