Circular economy initiatives focus on technologies related to reuse, recycling, and remanufacturing, which aim to recover waste and prevent environmental pollution resulting from improper disposal. One green approach within this framework involves synthesizing nanoparticles using biowastes like stems, leaves, seeds, pulp, stubble, bagasse, wood forest, flours, cereals, animal remains, manure, algal, and microorganisms. This approach is recognized for its low energy consumption and cost-effective production. The composition of the raw materials influences the nanoparticles’ final application, which spans various fields and can even be utilized within agriculture itself. Nanobiowastes can be grouped into two principal types: inorganic (nanosilica and nanometallics), and organic (nanocellulose, nanolignin, nanocarbons, and carbon dots) nanoparticles. Green synthesis approaches for nanoparticles focus on several key factors: (i) employing eco-friendly reducing agents, (ii) selecting a solvent, (iii) employing non-toxic and biocompatible materials for synthesis, (iv) ensuring facile and low-energy processing, and (v) enabling scalability of synthesis methods. Indeed, the steps taken to produce nanomaterials using biowaste aim to establish a sustainable and valuable circular economy. This approach holds immense potential for fostering economic and social growth, especially in countries where food security is of paramount importance for the future. By harnessing biowaste to create nanomaterials, we not only mitigate waste but also generate valuable resources that can be utilized in various sectors, thereby contributing to a more resilient and sustainable future. This chapter aims to delve into the properties of biowastes, exploring their utilization as bionanomaterials and the myriads of potential applications they offer.