Plant-derived bioactive polysaccharides (PDBPs), versatile polymers originating from various botanical sources, exhibit a spectrum of biological functionalities crucial for human health. This review delves into the multifaceted roles of these bioactive compounds, elucidating their immune-boosting properties, antioxidant prowess, anti-inflammatory capabilities, and contributions to gut health. Amidst their pivotal roles, the efficiency of PDBPs delivery and bioavailability in the human system stands as a central determinant of their efficacy and utilization. This review paper extensively and systematically examines the diverse biological activities, such as immunomodulatory effects, delivery mechanisms like microencapsulation, and promising applications of PDBPs within the realms of both food (functional foods and nutraceuticals) and pharmaceutical (antimicrobial agents and anti-inflammatory drugs) sectors. Additionally, it offers a comprehensive overview of the classification, sources, and structural diversity of these polysaccharides, highlighting various identification techniques and rheological considerations. Moreover, the review addresses critical safety and regulatory concerns alongside global legislation about plant bioactive polysaccharides, envisaging a broader landscape for their utilization. Through this synthesis, we aim to underscore the holistic significance of PDBPs and their potential to revolutionize nutritional and therapeutic paradigms.