While nanomaterials are increasingly being proposed for contaminant remediation, a major challenge is how to develop high removal functionality while maintaining low cost and environmental friendliness. In this study, a hybrid reduced graphene oxide/iron nanoparticle (rGO/Fe NPs) was prepared via the in situ reduction of GO and FeCl by eucalyptus leaf extract in one-pot. The obtained rGO/Fe NPs could rapidly remove 72.7% of Pb(II) from aqueous solution in 10 mins and remove up to the maximum removal efficiency of 82.4%. Electron microscopy, XPS and BET showed that the irregular FeO nanoparticles, sized between 20 and 40 nm, were disorderly dispersed on rGO sheets, which constituted a mesoporous material. FTIR and XRD indicated that the surface of rGO/Fe NPs was capped by many active organic constituents from the eucalyptus leaf extract. rGO/Fe NPs also showed a high selectivity for Pb(II) with minimal interference from either calcium or magnesium ions in the solution. Finally, GC-MS separated 13 significant active organic constituents from the eucalyptus leaf extract that possibly contributed to the reduction of rGO/Fe NPs. Overall, eucalyptus leaf extracts, acted efficiently as green reducing agents and impacted reactivity of the final material by determining the components and surface properties of rGO/Fe NPs.