To obtain a dielectric elastomer with excellent dielectric properties and actuated strain, we used bio-inspired dopamine to functionalize the surface of barium titanate (BT) particles. X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to confirm that a poly(dopamine) (PDA) layer of ca. 3.0 nm had been successfully deposited on the surface of the barium titanate particles. With the introduction of the PDA layer, the compatibility between the barium titanate filler and the elastomer matrix (hydrogenated nitrile-butadiene rubber) was significantly improved, which also resulted in the composites displaying better filler dispersion, higher dielectric constant, lower dielectric loss, and higher electric breakdown field compared with composites filled with pristine BT particles. Furthermore, the composites filled with PDA-coated BT (BT–PDA) exhibited higher electromechanical sensitivity (β) than the composites filled with pristine BT, leading to increased actuated strains. Nevertheless, the β of composites filled with pristine BT decreased with increasing content of filler, resulting in decreased actuated strains. Finally, a large actuated strain of 20% without any prestrain was achieved by the composite filled with BT–PDA, which is 54% larger than the largest actuated strain of the polymer without functionalized filler. Moreover, the dopamine functionalization method is simple, efficient, nontoxic, and easy to control, and can be used as a general strategy for improving the dielectric constant, breakdown strength, and actuated strain of dielectric elastomers.