Biofriendly green sustainable nanocatalyst Au@NiAg with high catalytic activity was prepared for hydrogenation and degradation of aquatic contaminants such as 4-nitrophenol (4-NP), Methyl Orange (MO), and Orange G (OG). Synthesized Au@Ni nanoparticles have a triangular shape while the Au@NiAg nanoparticles are of spherical shape and of smaller size, attributed to the digestive ripening of the Au@Ni where silver ion was deposited on the host Au@Ni nanoparticle surface. The Au@NiAg nanoparticles catalyzed hydrogenation of 4-nitrophenol and reduction of organic dyes follow Langmuir-Hinshelwood kinetics. The Au@NiAg nanoparticles have shown excellent catalytic activity with activity factors of 3167s(-1)g(-1), 5476s(-1)g(-1), and 3810 s(-1) g(-1) for 4-NP, MO, and OG, respectively. Silver nanoparticles act as cocatalyst for overall improvement of the performance of Au@NiAg. Above all the involvement of leaf extract mediated synthesis will open up an area to the production of sustainable, ecofriendlym and nontoxic core-shell nanocatalysts with exemplary catalytic activity.