Our report describes RAFT copolymerization of multiple species of active peptide monomers with N-(2-hydroxypropyl(methacrylamide) (HPMA) under aqueous conditions. Resulting statistical copolymers are narrowly disperse with highly controlled molecular weight and composition. Side-chain peptide copolymers were synthesized using a DNA condensing peptide (K-12), and an endosomal escape peptide (K6H5) that had been modified with an aminohexanoic linker and capped with methacrylamide vinyl on the NI-I terminus. Copolymers of HMPA-co-K-12 and HPMA-co-K-12-co-K6H5 efficiently condensed DNA into small particles that maintain size stability even in 150 mM salt solutions. With increasing peptide content, the peptide-based polymers demonstrated gene delivery efficiencies to HeLa cells that were comparable to branched polyethylenimine.