Silica nanoparticles have potential applications in diverse fields, such as construction, pharmaceuticals, batteries, and catalysis. Commercially, these are synthesized using some alkoxysilane precursors that are costly, toxic, and make the whole process expensive and polluting. Therefore, the development of some environmental-friendly approaches are encouraged for the safe synthesis of cost-efficient, green silica nanoparticles. Several silica-rich agricultural waste materials (corn cob, coffee husk, rice husk, sugarcane bagasse, wheat husk, etc.) have been recognized as invaluable, renewable resources to prepare silica nanoparticles. The objective of this chapter is to present an overview of the synthesis methods for green silica nanoparticles from different agricultural waste materials and their application as catalysts as well as catalyst support in various industrially important organic transformations occurred in the past decade. This chapter introduces to the various agricultural wastes, different methodologies (conventional as well as green) adopted for the synthesis of silica nanoparticles.