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The avocado processing industry produces up to 1.3M tons of agro-waste annually. Chemical analysis of avocado seed waste (ASW) revealed that it is rich in carbohydrates (464.7 ± 21.4 g kg−1) and proteins (37.2 ± 1.5 g kg−1). Optimized microbial cultivation of Cobetia amphilecti using an acid hydrolysate of ASW, generated poly(3-hydroxybutyrate) (PHB) in a 2.1 ± 0.1 g L−1 concentration. The PHB productivity of C. amphilecti cultivated on ASW extract was 17.5 mg L−1 h−1. The process in which a novel ASW substrate was utilized has been further augmented by using ethyl levulinate as a sustainable extractant. This process achieved 97.4 ± 1.9 % recovery yield and 100 ± 1 % purity (measured by TGA, NMR, and FTIR) of the target PHB biopolymer, along with a high and relatively uniform PHB molecular weight (M w = 1831 kDa, M n = 1481 kDa, M w /M n = 1.24) (measured by gel permeation chromatography), compared to PHB polymer extracted by chloroform (M w = 389 kDa, M n = 297 kDa, M w /M n = 1.31). This is the first example of ASW utilization as a sustainable and inexpensive substrate for PHB biosynthesis and ethyl levulinate as an efficient and green extractant of PHB from a single bacterial biomass. [Display omitted] • Avocado seed waste (ASW) was found to be a novel carbohydrate-rich source. • ASW was found as an efficient substrate for poly(3-hydroxybutyrate) (PHB) production. • Ethyl levulinate is a novel, cost-effective, and sustainable PHB extraction solvent. • High PHB recovery yield (~97 %) and purity (~100 %) were obtained. • High and uniform M w (1830 kDa, M w /M n = 1.23) PHB polymer was recovered. [ABSTRACT FROM AUTHOR]