Manipulating the size and shape of noncovalent multivalent assemblies is an ongoing challenge in the field of supramolecular polymers. Following a mechanistic approach, we reasoned that nucleation-elongation kinetics presents unique opportunities for controlled growth since the final outcome is likely to depend on the structure and dynamics of critical-nucleus formation. Taking fibrillar assembly of amyloid beta (A beta) peptide as the model system of nucleation-dependent supramolecular polymerization, here we report multivalent polymer-peptide conjugates (mPPCs) that redirect fibrillar assembly of A beta to form discrete nanostructures. The mPPCs were rationally designed to target A beta intermediates formed prior to critical nucleation. Atomic force microscopy and transmission electron microscopy studies show that in the presence of mPPCs, A beta self-assembles into zero-dimensional discrete nanostructures with lateral dimensions approximately in 5-35 nm, while A beta alone self-assembles into one-dimensional fibrils in micrometer. Thioflavin T kinetics fluorescence assays demonstrate that mPPCs suppress A beta fibrillogenesis. The mPPCs may thus represent a prototypical molecular design of multivalent macromolecules able to control the final shape of supramolecular polymers assembled via a nucleation-dependent mechanism.