Enhancing crop productivity and soil fertility has driven extensive research into novel approaches for fulfilling demand via sustainable agricultural practices. The present chapter explores the emerging field of microbial biosynthesis as a sustainable and eco-friendly strategy for the synthesis of biostimulant nanomaterials (NMs) and nanofertilizers (NFs). Microorganisms, like bacteria and fungi, are studied for their unique ability to synthesize nanoparticles (NPs) with explicit properties valuable for plant growth and nutrient uptake. Present study provides an overview of the current challenges in agriculture, including nutrient deficiencies, soil degradation, and environmental concerns associated with traditional fertilization practices. It also delves into the principles of microbial biosynthesis and its impending applications in the production of biostimulant NMs. The complex processes involved in microbial-mediated nanoparticle synthesis, including extracellular and intracellular mechanisms, are discussed to understand the mechanism associated. The subsequent sections highlight the diverse types of biostimulant NMs and NFs generated through microbial biosynthesis, emphasizing their unique physicochemical characteristics and their impact on plant growth and development. Case studies and experimental findings showcase the efficacy of these microbial-derived NMs in promoting seed germination, root progression, and nutrient assimilation. Environmental sustainability of microbial biosynthesis, highlighting its potential to mitigate the ecological footprint accompanying conventional fertilizer production has also been discussed. The regulatory aspects, safety considerations, and future prospects of integrating microbial biosynthesized NMs into normal agricultural practices are also debated. Keen review of literature concludes the microbial synthesis of NMs is a promising avenue for the fabrication of biostimulant NMs.