The rapid rise in demand for sustainable agriculture has fueled interest in innovative, eco-friendly approaches to enhance productivity amid climate change and environmental stressors. Among recent advances, green nanoparticles, nanomaterials synthesised via biological routes, have emerged as promising agents for promoting crop productivity and mitigating abiotic and biotic stresses. Plant-mediated nanoparticles, such as metal and metal oxide nanoparticles, have highlighted their roles as a promising alternative to conventional chemical fertilizers and pesticides, due to their superior effectiveness, minimal toxicity, and eco-friendly nature. The physicochemical properties and the mechanisms by which green nanoparticles improve nutrient use efficiency, stimulate plant hormonal dynamics, and bolster antioxidative defense systems. The impacts of green nanoparticles on germination, root and shoot elongation, photosynthetic efficiency, and nutrient assimilation are well discussed, showcasing their potential in yield enhancement and vegetative growth. Furthermore, this review also elucidates their function in modulating oxidative stress, activating defense pathways, and conferring tolerance against drought, salinity, heavy metals, and pathogen attacks by influencing plant physiological, molecular, and metabolic responses. By integrating recent findings, this review highlights the dual advantage of green nanoparticles: enhancing crop productivity while minimizing environmental footprint. The challenges related to nanoparticle biosafety, large-scale application, and regulatory frameworks are also addressed. The article concludes by outlining future research directions aimed at harnessing green nanotechnology to achieve sustainable crop production and global food security.