The development of biobased polymers to substitute their current petroleum-based counterparts is crucial for fostering a sustainable plastic industry. Here we report the biosynthesis and characterization of a group of biopolymers, poly(ester amide)s (PEAs), in Escherichia coli. PEAs are biosynthesized by constructing a new-to-nature amino acid polymerization pathway, comprising amino acid activation by β-alanine CoA transferase and subsequent polymerization of amino acyl-CoA by polyhydroxyalkanoate synthase. The engineered E. coli strains harboring this pathway are capable of biosynthesizing various PEAs, each incorporating different amino acid monomers in varying fractions. Examination of the physical, thermal and mechanical properties reveals a dependence of molecular weight on the type of polyhydroxyalkanoate synthase, a decrease in melting temperature and crystallinity as the 3-aminopropionate monomer fraction increases and enhanced elongation at break compared to its polyester analog. The engineered bacterial system will prove beneficial for the biobased production of various PEAs using renewable resources.