<p>This study examines the green synthesis of silver nanoparticles using mixed fish waste and their application as nano-fertilizers in agriculture. Disposed fish waste decay in the soil and cause soil, water, and air pollution. It is high time that these wastes are used to yield a value-added product. This is the first report of synthesizing silver nanoparticles from mixed fish wastes and using them as nano-fertilizer through foliar application for evaluating their effect on the growth, biochemical characters, number of nodules, and yield of two crop plants, chickpea (<i>Cicer arietinum</i> L.) and horse gram (<i>Macrotyloma uniflorum</i> L<i>.</i>). This approach reduces the damage caused by the extensive use of chemical fertilizers and supports sustainable agriculture. The silver nanoparticles synthesized using fish waste extracts were characterized by UV–visible spectro-photometer, XRD, Transmission electron microscopy, and scanning electron microscopy to confirm their synthesis, size, and morphology. The synthesized nanoparticles were used as a nano-fertilizer through foliar spray on the test plants and found to improve the growth and yield of the tested plants compared to the control. From this study, we conclude that foliar application of AgNPs synthesized by fish waste extract continuously supplies nutrients for the sustainable growth of test plants.</p> Graphical abstract <p></p>