A route of synthesizing triblock terpolymers in a one-pot, one-step polymerization approach is presented. The combination of two distinct polymerization techniques through orthogonal catalyst/initiator functionalities attached to a polymeric linker furnishes novel pathways to ABC-terpolymers. Both polymerizations have to be compatible regarding mechanisms, chosen monomers, and solvents. Here, an ,-heterobifunctional poly(ethylene glycol) serves as polymeric catalyst/initiator to obtain triblock terpolymers of poly(norbornene)-b-poly(ethylene glycol)-b-poly(l-lactic acid) PNB-PEG-PLLA via simultaneous ring opening metathesis polymerization and ring opening polymerization in a fast one-pot polymerization. Structural characterization of the polymers is provided via H-1-, DOSY-, and H-1,H-1-COSY-NMR, while solution and thin film self-assembly are investigated by dynamic light scattering and atomic force microscopy.