We demonstrated the photoredox catalytic activity of iodine-functionalized polydopamines (IPDAs) with varying iodine contents under green- and red-light irradiation in aqueous solution. IPDAs were readily prepared through postpolymerization iodination of PDA and characterized by X‒ray photoelectron spectroscopy, UV‒vis spectroscopy, FT‒IR spectroscopy, and dynamic light scattering. Compared with intact PDA, IPDAs exhibited enhanced photocatalytic performance in radical photopolymerization of water-soluble acrylate monomers in the presence of triethanolamine. In particular, I₁₅PDA showed the highest activity under both green and red light, whereas intact PDA was essentially inactive under red-light irradiation. Kinetic analysis, reaction quantum yield, initiation efficiency, and monomer-scope studies consistently confirmed the superior catalytic performance of I₁₅PDA. Phosphorescence intensity increased with iodine content, indicating enhanced intersystem crossing via the heavy-atom effect. These findings establish iodine functionalization as an effective strategy to enhance the photoredox activity of PDA and provide fundamental mechanistic insights that enable the rational design of melanin-inspired organic photocatalysts.