A new type of functional supramolecular assembly is formed by combining cationic porphyrin (TAPP) and the anionic generation 7.5 (G7.5) poly(amidoamine) (PAMAM) dendrimer in aqueous solution at basic pH. The interplay of noncovalent interactions is used as a key to control the formation of supramolecular structures and thereby to improve the photocatalytic activity of the porphyrin. The porphyrin dendrimer assemblies show pH responsiveness. Their size, shape, and internal structure are controlled by varying the loading ratio. Structures were analyzed by light scattering, small-angle neutron scattering, zeta-potential measurements, UV/vis and fluorescence spectroscopy, and atomic force microscopy. The assemblies show structures with high quantum yield which makes them suitable for light harvesting processes, for example, in solar energy conversion. As a photocatalytic model reaction, the degradation of the anionic dye methyl orange is investigated, showing differing interaction withthe assembles based on their charge. A substantially enhanced photocatalytic activity was found.