A new type of catalytically active self-assembled nanostructures in aqueous solution is presented. Polyelectrolyte-porphyrin nanoscale assemblies consisting of anionic cylindrical poly(styrene sulfonate) brush molecules and cationic tetravalent meso-tetrakis(4-N-methyl-pyridinium)porphyrin (TMPyP) or meso-tetrakis(4-(trimethyl-ammonium)phenyl)-porphyrin (TAPP), respectively, exhibit up to 8-fold higher catalytic activity with regard to light induced iodide oxidation than the corresponding porphyrins without polymeric template. This is particularly interesting because a general concept rather than a specific binding motif is exploited. The approach introduced here hence is attractive due to its facility and versatility and bears potential, for example, in light harvesting and energy conversion.