An enhanced method of synthesizing silver nanoparticles (AgNPs) is adopted herein using the aqueous extract of Decalepis hamiltonii root as both reducing and capping agents. In the recent years, metal nanoparticles have been actively synthesized using green route which is considered as an efficient, inexpensive and eco-friendly method. The generation of AgNPs was first observed from the UV–visible spectroscopy. The XRD analysis confirms the FCC structure with an average crystal size of 22 nm which is calculated using Scherrer’s formula. The functional group responsible for the reduction of AgNPs is identified from the FTIR analysis. Transmission electron microscopy (TEM) showed the formation of silver nanoparticles of size ranging from 5 to 20 nm with few agglomerations. The antibacterial studies were carried out against the Escherichia coli and Staphylococcus aureus using minimum inhibitory concentration (MIC) technique. The third-order nonlinear optical properties of AgNPs were measured by the Z-scan technique. The negative nonlinearity observed was utilized for the study of optical limiting behavior. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.