Polyhydroxyalkanoates (PHAs) are a unique class of commercially manufactured biodegradable polyesters with properties suitable for partially substituting petroleum‐based plastics. However, high costs and low volumes of production have restricted their application as commodity materials. In this study, tri‐metallic complexes were developed for carbonylative polymerization via a dual catalysis strategy, and 17 products of novel PHAs with up to 38.2 kg mol−1 Mn values were discovered. The polymerization proceeds in a sequential fashion, which entails the carbonylative ring expansion of epoxide to β‐lactone and its subsequent ring‐opening polymerization that occurs selectively at the O‐alkyl bond via carboxylate species. The wide availability and structural diversity of epoxide monomers provide PHAs with various structures, excellent functionalities, and tunable properties. This study represents a rare example of the preparation of PHAs using epoxides and carbon monoxide as raw materials. A dual catalysis strategy via carboxylate species featuring weak nucleophilicity and basicity is used for the direct carbonylative polymerization of various epoxides for the production of original advanced polyhydroxyalkanoates (PHAs) with high molecular weight and tunable functionalization. This study represents a rare example of PHAs synthesis using epoxides and carbon monoxide as raw materials.