This review covers the development of the in situ growth of polymers from biomolecules, also termed the “grafting from” conjugation methodology. We trace the evolution of this field of research, with an emphasis on recently developed methods to synthesize polymer conjugates of peptides and proteins with control over the site of conjugation, the stoichiometry of the conjugate, and the chain length and polydispersity of the polymer. We highlight the functional properties and potential biomedical applications of the peptide/protein–polymer conjugates, including conjugates with more advanced architecture and self-assembly behaviour.