The untapped potential of marine environments offers a vast reservoir of unique microorganisms with novel metabolic pathways, paving the way for innovative biotechnological applications. Streptomyces strains isolated from the marine environment of the Bay of Bengal, Odisha, India, were screened for polyhydroxybutyrate (PHB) synthesis where S. nigra KDS4 showed the highest PHB accumulation. PHB is a bioplastic synthesized by microorganisms and it offers a sustainable, versatile, and eco-friendly alternative to traditional plastics, addressing both environmental and functional challenges across various industries. Optimized conditions (pH 7.5, salinity 2.5%, temperature 30.6°C, and 6-day incubation) and a starch-to-KNO₃ ratio of 20:1 enhanced the biomass (3.95 g/L) and PHB accumulation (2.63 g/L), as determined via response surface methodology (RSM). The elemental composition and surface morphology of PHB were determined using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy (FESEM-EDX). The biophysical characterization identified the major functional groups (carbonyl, methyl, methylene), and the chemical profiling through GC-MS revealed different compounds (2,4-di-tert-butylphenol, n-hexadecanoic acid, octadecenoic acid) present in the polymer. PHB exhibited a tensile strength of 0.61 Kg/mm2, and elongation at break of 15%. The biodegradability of the PHB film was assessed, showing 92.3% degradation within 30 days. Further, the biocompatibility of the PHB was confirmed using HaCaT cell line showing 82.40 to 72.84% cell viability, demonstrating its potential for various applications. The utilization of marine Streptomyces for bioplastic production, and other high-value applications represents a promising avenue for addressing global sustainability challenges while advancing the principles of the blue economy. Keywords: Marine bacteria, Streptomyces nigra KDS4, PHB synthesis, Bioplastic, Blue Economy, Sustainability