Silver nanoparticles possess a wide range of applications especially in the field of medicine and this has stimulated the need for synthesizing them. Conventionally, chemical methods are used, which are hazardous and energy consuming. Therefore an eco-friendly and facile means of synthesizing nanoparticles is needed to replace the chemical method of synthesis. In the present study, silver nanoparticles were synthesized in a cost-effective and environment-friendlymanner using aqueous leaf extract of Ailanthus excelsa—a medicinal tree used in the treatment of asthma, bronchitis, cold, abdominal pain, etc. The leaf extract helped in the bioreduction of silver ions yielding silver nanoparticles. The silver nanoparticles thus biosynthesized were characterized using UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy (SEM). These biologically synthesized silver nanoparticles were also found to exhibit excellent antibacterial effect against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumonia and anticancer effect against MCF-7 cell line.