In this communication, we report a catalyst-free methodology for single unit monomer insertion (SUMI) into reversible addition–fragmentation chain transfer (RAFT) agents initiated by low intensity visible light. This method is applicable to broad range of monomer families (monosubstituted vinyl monomers) and allows for the preparation of the corresponding single monomer insertion product in high yields (typically >90%; isolated yields after chromatography 60–80%). The fidelity of the end-functional SUMI products is demonstrated with use of the SUMI products in RAFT polymerization and by using the tools of conventional chemistry (thiol–ene and esterification reactions). A uniform oligomer comprising five discrete vinyl monomer repeat units was synthesized by an iterative strategy comprising three consecutive SUMI reactions and two intermediate esterification and thiol–ene steps. We thus demonstrate a new protocol for incorporating the rich functionality of available vinyl monomers into polymers where sequence is precisely defined at the monomer level.