The growing demand for sustainable and environment-friendly materials has driven extensive research on biopolymers for applications in agriculture, food science, and environmental remediation. Among these, nanocellulose-hydrogel hybrids (NC-HHs) have gained significant attention as an innovative class of bio-based materials that uniquely combine the remarkable physicochemical properties of nanocellulose with the functional versatility of hydrogels. These hybrids are characterised by exceptional water retention, mechanical strength and biodegradability, enabling advances in precision agriculture, smart food preservation and contaminant remediation. This review provides a comprehensive understanding of the synthesis, properties, and multifunctional applications of NC-HHs, emphasising their innovative role in sustainability. In agriculture, NCHHs enhance soil moisture retention, support plant growth, and serve as carriers for controlled-release fertilizers, optimizing water and nutrient use efficiency. In the food industry, they enable intelligent packaging solutions that extend shelf life, monitor food freshness, and inhibit microbial growth. Additionally, NC-HHs present groundbreaking strategies for environmental remediation by effectively immobilizing pollutants in water and soil. Beyond summarizing recent advances, this review presents an in-depth mechanistic perspective on the interactions between NC and HH, critically evaluating their structure-property relationships, functional adaptability and application-specific performance. By integrating recent advances in nanocellulose functionalisation, polymer chemistry and the development of responsive hydrogels, this review critically examines the key technological innovations and future prospects of NC-HHs, underscoring their transformative potential in addressing global challenges related to food security, environmental sustainability, and sustainable agricultural practices.