A bioderived plasticizer for biopolymers includes a compatibilizing unit and a polyester plasticizing unit. The plasticizer improves the flexibility of biopolymers while not adversely affecting their modulus. The compatibilizing unit renders the plasticizer more miscible with the desired base biopolymer and includes a lower alkyl (C3 to C7) organic acid. The polyester plasticizing unit is formed from monomers comprising a multifunctional alcohol and an aliphatic anhydride or its equivalent dicarboxylic acid and ester derivatives. The polyester plasticizing unit may optionally include one or more difunctional alcohols in combination with the multifunctional alcohol. The resulting the bioderived plasticizer has a low glass transition temperature (Tg), preferably between −20° C. to 30° C. The plasticizer is preferably amorphous.