Single-atom catalysts (SACs) combine the best of two worlds by bridging heterogeneous and homogeneous catalysis. The superior catalytic properties of SACs, however, can hardly be exploited without a suitable substrate. Here, we explore the possibility of using hybrid organic-inorganic perovskites as supporting materials for single transition-metal atoms. By means of first-principles calculations, we predict that single Pt atoms can be incorporated into methylammonium lead iodide surfaces by replacing the methylammonium groups at the outermost layer. The iodide anions at the surface provide potentially uniform anchoring sites for the Pt atoms and donate electrons, generating negatively charged Pt_{1}^{δ-} species that allow for preferential O_{2} adsorption in the presence of CO. Such Pt sites are able to catalyze CO oxidation and may also play a role in CO_{2} reduction. The fundamental understanding generated here will shed light on potential applications of hybrid perovskites in the field of (photo)catalysis.