The ring‐opening alternating copolymerization (ROAC) of biorenewable glycidyl ethers with 3,4‐dihydrocoumarin (DHC) was achieved by using metal‐free Lewis pair as catalyst. This mild process provided access to renewable polyesters with perfectly alternating structures and functional groups fidelity. Remarkably, we observed highly regioregular arrangement of substituents along with poly(phenol ether‐alt‐ester) backbone. A one‐step strategy to block copolymer could also be realized by terpolymerization of DHC, epoxides with cyclic anhydrides via pre‐rate‐determining selectivity. Post‐polymerization modification of the resultant polyesters was further performed by thiol‐ene click reaction of vinyl, Diels–Alder reaction of furyl, cleavage reaction of benzyl ethers and tetrazine click reaction. By incorporating two different pendant functional groups into a copolymer, combinatorial and selective functionalization was achieved for introducing additional functionality, giving a route to highly modifiable polyesters. Therefore, this work provides a paradigm for designing functional and regioregular polyesters as a green synthetic toolbox derived from organocatalysis and renewable feedstocks.