Currently, sustainability initiatives that use green chemistry to improve and/or protect our global environment are becoming focal issues in many fields of research. Instead of using toxic chemicals for the reduction and stabilisation of metallic nanoparticles, the use of various biological entities has received considerable attention in the field of nanobiotechnology. Among the many possible natural products, polysaccharides and biologically active plant products represent excellent scaffolds for this purpose. Polysaccharides have hydroxyl groups, a hemiacetal reducing end, and other functionalities that can play important roles in both the reduction and the stabilisation of metallic nanoparticles. Among the various categories of compounds in plants that have potent biological activities, phytochemicals are emerging as an important natural resource for the synthesis of metallic nanoparticles. The focus of this review is the application of polysaccharides and phytochemicals in the green synthesis of gold and silver nanoparticles to afford biocomposites with novel uses in nanomedicine and as nanocomposites.