The global demand for sustainable and health-enhancing feed additives has catalysed interest in single-cell protein (SCP) enriched with polyhydroxyalkanoates (PHAs), which holds potential as an effective replacement to antibiotics. PHAs-rich SCP offers a unique convergence of high-quality protein and biodegradable biopolymers with nutraceutical properties, presenting a promising alternative to conventional feed sources. This review explores the potential of PHAs-rich SCP as a novel nutraceutical feed ingredient, highlighting its microbial sources, production strategies, compositional advantages, dual functionality as both protein source and bioactive compound and current challenges & future prospect. Emphasis is placed on its nutraceutical roles including immunomodulatory, antioxidant, and gut health-promoting effects, alongside environmental and economic benefits. Furthermore, this article aims to provide a comprehensive insight into the multifaceted value of PHAs-rich SCP, advocating its role in promoting sustainable and health-oriented animal nutrition.