The synthesis of polyesters with the desired functional groups without additional protection and deprotection steps remains a worthwhile challenge to polymer chemists. Herein, we put forward a solution for the direct preparation of green copolyesters with versatile functionalities via the cascade polycondensation-coupling ring-opening polymerization (PROP) using a biobased cyclic diester ethylene brassylate as the monomer and functional diols/polyether diols as initiators. The combination of two polymerization processes into one system enables the facile synthesis of biodegradable polyesters with versatile functionalities, including alkane, alkene, alkyne, aromatic, halide, ether, and amide functional groups, and poly(ether ester) multiblock copolymers, together with high functional group contents (50% molar ratio to brassylate) and relatively high molecular weights (up to 6 × 10⁴ Da). The cascade strategy provides a feasible method for the synthesis of high functional group content polyesters with tailor-made properties, highly effective for post-modifications that are suitable for a variety of applications.