Display omitted ► Metallic NPs are synthesized for the first time using Anacardium occidentale. ► Both leaf extract and powder are used for the biosynthesis. ► Formation of Au core–Ag shell bimetallic nanoparticles is reported. ► The possible bio-molecule responsible for reduction and stabilization is suggested. ► The method is a simple, efficient and environment-friendly approach. Present study reports a green chemistry approach for the biosynthesis of Au, Ag, Au–Ag alloy and Au core–Ag shell nanoparticles using the aqueous extract and dried powder of Anacardium occidentale leaf. The effects of quantity of extract/powder, temperature and pH on the formation of nanoparticles are studied. The nanoparticles are characterized using UV–vis and FTIR spectroscopies, XRD, HRTEM and SAED analyses. XRD studies show that the particles are crystalline in the cubic phase. The formation of Au core–Ag shell nanoparticles is evidenced by the dark core and light shell images in TEM and is supported by the appearance of two SPR bands in the UV–vis spectrum. FTIR spectra of the leaf powder before and after the bioreduction of nanoparticles are used to identify possible functional groups responsible for the reduction and capping of nanoparticles. Water soluble biomolecules like polyols and proteins are expected to bring about the bio-reduction.