The effectiveness of the sandwich beam structure on vibration attenuation has been extensively investigated in diverse engineering applications. As the evolvement of the metamaterial structure into sandwich beam can further improve the vibration attenuation performance, a novel metamaterial magnetorheological elastomer (MRE) sandwich beam (MMRESB) in a compact design was proposed in this study to generate a real-time tunable local resonance band gap for vibration isolation. The controllable band gap behavior and the transmission spectrum were investigated theoretically based on the Timoshenko beam theory and the transfer matrix method. Subsequently, experiments were conducted to evaluate the controllability of the band gap and its vibration transmissibility properties. The results show that as the applied current increases from 0.0 A to 1.0 A, the compact MMRESB with local coil resonators can autonomously tune its band gap from 52.3–92.8 Hz to 56.5–98.9 Hz, and that the compact MMRESB can significantly suppress the vibration wave propagation along the beam.