<p>Plant health represents a crucial interface connecting environment, animal, and human health within the One Health framework. The heavy reliance on agrochemicals in the past has raised concerns regarding environmental degradation, food safety, and ecosystem resilience. The One Health strategy for sustainable agriculture emphasizes the balance between productivity and ecological and human health safeguards. Seaweeds are high in polysaccharides, polyphenols, and metal binding compounds that are used as biogenic reducing and stabilizing agents that react to form nanoparticles with antimicrobial, biostimulant, and stress-alleviating properties. These nanoparticles derived from seaweed improve nutrient delivery, stimulate systemic resistance, and enhance soil microbiome balance, thus improving crop productivity and biotic and abiotic stress tolerance. Aside from agriculture, their multifunctionality supports One Health goals through reduced dependence on agrochemicals, enhanced soil and ecosystem quality, and food safety. This review integrates recent advancements in seaweed mediated nanotechnology and its potential for climate-smart and sustainable agriculture aligned with global health and environment agendas.</p>