Crystallized silver nanoparticles (AgNPs) were synthesized by using the eco-friendly Artocarpus heterophyllus biomaterial. The synthesis of AgNPs was a green approach and a rapid method. The AgNPs were characterized by field-emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy, X-ray diffraction and inductively coupled plasma atomic emission spectroscopy. The FE-SEM analysis showed that the size of the synthesized AgNPs ranged around 45 nm. The plant leaves acted as both a reducing and a capping agent. The synthesized AgNPs showed an absorption peak at 400–440 nm. The biosynthesized AgNPs were tested for their antimicrobial activity against both the gram-positive bacterium Staphylococcus aureus and the gram-negative bacterium Escherichia coli and the fungus Aspergillus niger. The method used in the present work is simple, rapid, single-step, environment-friendly and very cheap and is an alternative to the current physicochemical methods. The antimicrobial activity of biosynthesized AgNPs suggests their possible application in the medical and pharmaceutical industry.