We report a new strategy that uses N-trimethylsilyl (N-TMS) amine to mediate controlled ring-opening polymerization of amino acid N-carboxyanhydrides (NCAs). This polymerization proceeds via a unique, trimethylsilyl carbamate (TMS-CBM) propagating group that results from the cleavage of the Si-N bond of N-TMS amine followed by NCA ring opening. Propagation of the polypeptide chains proceeds through the transfer of the TMS group from the terminal TMS-CBM to the incoming monomer followed by the formation of a new TMS-CBM propagating group. Formation of the TMS-CBM was confirmed by MS and NMR. Polypeptides formed by the N-TMS amine-mediated polymerization have the expected molecular weights, narrow molecular weight distributions, and controlled functional groups at the C-termini of the polypeptides.