CaCO₃ crystallization behavior was studied in the presence of a thermo-responsive polypeptide copolymer, poly(N-isopropyl acrylamide)-b-poly(L-glutamic acid) (PNIPAM-b-PLGA). At lower temperatures, the copolymer dissolved well and the unimers mediated the formation of rosette-like calcite crystals through a mesoscale assembly process. At higher temperatures, the copolymer self-assembled into micelles with PNIPAM as the core and PLGA as the shell. The micelles mediated the formation of coral-like aragonite fiber clusters at a high micelle concentration, while fewer aragonite fibers were generated at a low concentration and vaterite crystals were obtained instead of aragonite. The time-resolved experiment revealed that the aragonite fibers were formed through a solution–precursor–solid (SPS) process via a transient polymer-induced liquid-precursor (PILP) phase. The new findings through the experiments can enrich our existing knowledge of biomimetic mineralization and provide useful information for designing functional materials.