The polycrystalline sample of a double perovskite, Sm 2NiMnO 6 was synthesized by a solid-state reaction route. From the X-ray structural study, it is found that the structure of the material is monoclinic with lattice parameters: a = 4.1750(63) Å, b = 7.6113(63) Å, c = 5.9896(63) Å, and β = 112.70°. These parameters are very close to and consistent with those of such type of materials. The dielectric, impedance, AC conductivity, and electrical modulus properties of the sample were studied in the temperature range of 25–300 °C and the frequency range of 1 kHz–1 MHz. Typical relaxor behavior observed in the dielectric studies was confirmed by Vogel–Fulcher fitting. From the Nyquist plots, the temperature dependent contribution of grain and grain boundary effect was confirmed. The non-Debye type of relaxation was found using the complex impedance spectroscopy. The magnetic study revealed that the sample had paramagnetic behavior at room temperature. Magneto-electric (ME) coefficient was obtained by changing DC bias magnetic field. This type of lead-free relaxor ferroelectric compound may be useful for high-temperature applications.