Terpolymers are used to generate bio‐decomposable self‐assemblies. PEG‐PVL‐PGMA terpolymers are synthesized via a combination of organocatalyzed living radical polymerization (RCMP) with polymerization‐induced self‐assembly (PISA), generating vesicle, multicompartment micelle (MCM), and core‐compartmentalized worm (CCW), where PEG, PVL, and PGMA are poly(ethylene glycol) monomethyl ether, poly(δ‐valerolactone), and poly(glycidyl methacrylate) and PGMA is grown during the PISA. MCM and CCW are uniquely obtainable using terpolymers. The PVL segment is biodegradable, and the obtained assemblies are bio‐decomposable. Heavy metal‐free and sulfur‐free synthesis and bio‐decomposability of the assemblies are attractive features.