We report a facile green approach for fabrication of Ag nanoparticles by room temperature bioreduction of Ag+ ions with aqueous Zingiber officinale extract. The surface plasmon resonance (SPR) peak of Ag nanoparticles, evident from optical absorption studies, red shifted and broadened upon sunlight irradiation. Atomic force microscopy studies showed that increase in Ag concentration and sunlight irradiation resulted in the growth of Ag nanoparticles and formation of Ag nanoparticle aggregates. The biosynthesized Ag nanoparticles exhibited strong antibacterial activity toward waterborne bacterium Escherichia coli. This work demonstrates a rapid, facile, and energy-efficient green synthesis of Ag nanoparticle dispersions with strong plasmonic response and enhanced antibacterial activity.