Polydopamine functionalized reduced graphene oxide-gold nanoparticle (PDA-RGO/Au) nanocomposites were successfully prepared by a simple and mild procedure. The PDA-RGO/Au nanocomposite is successfully formed in an aqueous buffer solution (pH 8.5) without using any reducing agent. FTIR confirmed the successful coating of PDA and informed the reduction of the surface functional groups of GO. The formation of reduced GO and Au NPs was further evidenced by UV-Vis and X-ray diffraction spectroscopy. This method is environmentally friendly and highly beneficial for the mass production of graphene-noble metal based nanocomposite. The as prepared PDA-RGO/Au nanocomposite could greatly enhance the electrochemical oxidation of nicotine. We fabricated an electrochemical nicotine sensor based on the prepared PDA-RGO/Au nanocomposite. The proposed nicotine sensor showed a wide detection range from 0.05 to 500 μM with a low detection limit of 0.015 μM. Moreover, the proposed nicotine sensor was also successfully applied for determination nicotine content in tobacco products.