Metallic nanocomposites are gaining considerable attention and are widely being implemented in several biomedical and engineering applications due to their potent physicochemical properties. To ease wide application of nanoparticles, research is focused on novel and better synthesis strategies. This brief chapter details on the biofabrication of diverse forms of metallic nanoparticles using various bacterial systems, and the cellular impact, illustrated using suitable examples. Demonstration on the biosynthesis of silver nanoparticles using the cell-free extract of P. plecoglossicida is presented. This chapter will also describe the influence of various physicocultural parameters such as the growth medium, concentration of precursor salt; pH and temperature on the biotransformation, so as to attain desirable morphological and surface characteristics of nanoparticles. Overall, this chapter aims to discuss the recent progress in relation to bacterial-based biosynthesis so as to have a better understanding on their safe use for various biomedical and engineering applications.