In this work, we utilize tobacco mosaic virus (TMV) as a bio-mediator to synthesize Ag nanoparticles in a controlled mannerunder mild aqueous conditions without chemical reducing agents,as shown in Scheme 1. Specifically, simple mixing of Ag pre-cursors in the form of Tollens’ reagent (Ag(NH3)2+) with TMVunder elevated temperature leads to consistent formation of Agnanoparticles within an hour. UV–vis and TEM analysis showsize-controlled synthesis of TMV-mediated Ag nanoparticles (withdiameter between 2 and 10 nm), following two-step Finke–Watzkymechanism (i.e. slow nucleation and fast autocatalytic growth)and further growth via secondary coalescence process in someconditions. The as-prepared particles exhibit both higher catalyticactivity for 4-nitrophenol hydrogenation and antibacterial activ-ity than previously reported values [16]. Combined these resultsillustrate the advantage of viral protein-mediated biofabricationapproach for controlled synthesis and improved functionalities forcatalysis and antibacterial activity.