Excellent electroconductivity, fire resistance, and mechanical properties are several important indexes for electromagnetic shielding sealing materials. In this work, a novel functionalized graphene decorated with a nickel-Schiff base (rGO-Salen-Ni) was first synthesized via a chemical modification process, and applied in enhancing the mechanical properties, electroconductivity, and fire resistance of a thermoplastic polyurethane elastomer (TPU). The experimental result illustrated that the rGO-Salen-Ni significantly improved the above vital properties of TPU. First, the tensile strength, elongation at break, and storage modulus of the TPU containing only 1.5 wt% rGO-Salen-Ni (TPU/rGO-Salen-Ni1.5) were respectively increased by 1.50 times, 1.58 times, and 2.17 times; second, the electrical conductivity of the TPU/rGO-Salen-Ni1.5 was increased by 5 orders of magnitude in comparison with that of a pure TPU, up to 7.3 × 10 −5 S m −1 ; finally, the TPU/rGO-Salen-Ni1.5 displayed excellent flame retardancy; for instance, the peak of heat release rate, total heat release, and total smoke production were respectively decreased by 43%, 22%, and 28% compared with the corresponding values of pure TPU. The analysis of the enhancement in mechanical properties and electroconductivity of TPU/rGO-Salen-Ni revealed that the uniform dispersion of rGO-Salen-Ni, resulting from the incorporation of the nickel-Schiff base into the GO, was the leading reason for their improvements. The study on the flame-retardant mechanism demonstrated that a more continuous and compact protective layer related to the nickel-Schiff base played the key role in the excellent fire resistance of TPU/rGO-Salen-Ni. The rGO-Salen-Ni shows great potential for application in electromagnetic shielding sealing materials. Excellent electroconductivity, fire resistance, and mechanical properties are several important indexes for electromagnetic shielding sealing materials.