The global agri-food sector faces unprecedented challenges in meeting the nutritional demands of a growing population while simultaneously reducing its substantial environmental footprint, which accounts for approximately one-third of anthropogenic greenhouse gas emissions and significant resource depletion. Microbial fermentation technologies have emerged as a cornerstone of sustainable food processing, offering transformative solutions that align with circular bioeconomy principles and climate resilience goals. This review provides a comprehensive examination of recent advances in microbial fermentation within agri-food systems, spanning from traditional practices to cutting-edge biotechnological innovations. The scope encompasses the functional roles of lactic acid bacteria, yeasts, and fungal cultures in food transformation, alongside engineered microbial consortia and synthetic ecology approaches that enhance process stability and productivity. Key technological advancements discussed include precision fermentation systems integrated with artificial intelligence-assisted optimization, comparative analysis of solid-state and submerged fermentation platforms, and innovations in downstream processing for metabolite recovery. Major applications are examined across functional food development, agro-residue valorization, plant-based protein alternatives, and climate-resilient food systems. The review further addresses techno-economic feasibility, regulatory frameworks, and sustainability assessment tools essential for industrial implementation. By synthesizing current knowledge and identifying strategic research directions, this paper concludes that microbial fermentation technologies represent a pivotal platform for achieving sustainable agri-food processing, waste minimization, and value addition within the broader context of global food security and environmental stewardship.