A high performance thermally expanded reduced graphene oxide (TErGO) nanocomposite decorated with Ni3CNi nanoparticles (TErGO/Ni3C-Ni) has been successfully synthesized by using a facile and eco-friendly approach. The morphology, textural features, surface composition and stability of TErGO/Ni3C-Ni nanocomposite are investigated by various physicochemical characterizations which revealed the uniform dispersion of crystalline metal nanoparticles inside TErGO matrix. The composite has been exhibited a large surface area and pore volume of 121 m(2) g(-1) and 0.791 cm(3) g(-1), respectively. The TErGO/Ni3C-Ni exhibited remarkable catalytic performance surpassing most metal-based catalysts with various kind of support matrices reported in recent literature. The reduction of Cr(VI) to Cr(III) was achieved within 1 min with an excellent rate constant of 2.74 min(-1) and phenomenally higher specific removal rate (SRR) of 0.29 mg Cr(VI) min(-1). mg(-1) of TErGO/Ni3C-Ni. While it also proved an excellent reducing catalyst for organic dyes via NaBH4 with full reduction achieved within 30 s. Moreover, as prepared nanocatalyst possesses excellent stability and recyclability with easy magnetic separation.