<p>This review focused on the recent developments in eco-friendly biosynthetic approaches for calcium oxide nanoparticles (CaO NPs) and their use in photocatalytic applications. However, the traditional approaches possess some limitations, including extreme experimental conditions, complex instruments, and hazardous chemicals. Hence, due to the rising need for greener approaches and perspective of nanomaterials in a variety of uses, CaO-NP synthesis through sustainable and eco-friendly clean processes has recently become the center of attention. This study presents detailed discussions about the fabrication of CaO NPs using plant and other biogenic assemblies and the parameters affecting their synthesis. This review discusses the excellent antimicrobial applications of CaO NPs, along with their mechanisms. Such NPs synthesized by green methods are very biocompatible. Additionally, green-synthesized CaO NPs have shown excellent catalytic, photocatalytic, and agricultural features. Therefore, researchers are provided with insight into the recent trends in the fabrication of CaO NPs through various biogenic assemblies and their potential applications.</p>