Derived from renewable feedstocks, such as biomass, polylactic acid (PLA) is considered a more environmentally-friendly plastic than conventional petroleum-based polyethylene terephthalate (PET). However, PLA must still be recycled and its growing popularity and mixture with PET plastics at the disposal stage poses a cross-contamination threat in existing recycling facilities and results in low-value and low-quality recycled products. Hybrid upcycling has been proposed as a promising sustainable solution for mixed plastic waste; but its techno-economic and lifecycle environmental performance remain understudied. Here we propose a hybrid upcycling approach using a biocompatible ionic liquid (IL) to first chemically depolymerize plastics, then convert the depolymerized stream via biological upgrading with no extra separation. We show that over 95% of mixed PET/PLA was depolymerized into their respective monomers, which then served as the sole carbon source for the growth of Pseudomonas putida, enabling the conversion of the depolymerized plastics into biodegradable polyhydroxyalkanoates (PHA). In comparison to conventional commercial PHA, the estimated optimal production cost and carbon footprint are reduced by 62% and 29%, respectively.