Abstract <p>Replacing petroleum-based plastics with sustainable alternatives requires economically viable biomanufacturing routes. This review comprehensively assimilates two critical pillars of bio-based polymer development: the microbial synthesis of lactic acid (LA) and its subsequent polymerization into polylactic acid (PLA). The first section critically examines advancements in the eco-friendly production of LA from renewable substrates through microbial fermentation. It highlights recent breakthroughs in metabolic engineering, process optimization, and cleaner downstream purification techniques to achieve high optical purity and yield. The second section focuses on the conversion of LA into PLA, detailing synthesis mechanisms via direct condensation and ring-opening polymerization (ROP). The manuscript evaluates the intricate relationships between PLA’s structural, thermal, and mechanical properties, alongside state-of-the-art processing technologies such as 3D/4D printing and electrospinning. By addressing prevailing bottlenecks—specifically the high cost of raw materials and the precise control of degradation rates—this review provides a strategic roadmap for the sustainable, large-scale production of PLA, aligning bio-based polymer development with shifting environmental and commercial demands.</p> Key points <p>• <i>Microbial routes boost sustainable, high-purity lactic acid production.</i></p> <p>• <i>Advances in PLA polymerization enhance material performance and applications.</i></p> <p>• <i>Lignocellulosic biomass enables low-cost, eco-friendly LA and PLA production.</i></p>