A six-membered cyclic carbonate derived from natural sugar D-mannose was prepared using CO2 as a C1 building block at room temperature and atmospheric pressure. The monomer was synthesized in two steps from a commercially available mannopyranose derivative. Polycarbonates were rapidly prepared at ambient temperature by controlled ring-opening polymerization (ROP) of the monomer, initiated by 4-methylbenzyl alcohol in the presence of 1,5,7-triazabicyclo[5.4.0]dec-5-ene (TBD) as the organocatalyst. Head-to-tail regiochemistry was indicated by NMR spectroscopy and is supported by DFT calculations. These aliphatic polycarbonates exhibit high-temperature resistance and demonstrate potential for postpolymerization functionalization, suggesting future application as high-performance commodity and biomedical materials.