We present a plasmon-active hybrid nanomaterial design with electrochemical tunability of the localized surface plasmon resonances. The plasmonic-active nanostructures are composed of silver nanocube aggregates embedded into an electrochromic polymer coating on an indium tin oxide electrode with the nanocube aggregation controlled by the surface pressure. Such polymer–nanocube hybrid nanomaterials demonstrated unique tunable plasmonic behavior under an applied electrochemical potential. A significant reversible experimental peak shift of 22 nm at an electrical potential of 200 mV has been achieved in these measurements. Finite-difference time-domain (FDTD) simulations show that, under full oxidation potential, a maximal spectral shift of ca. 80 nm can be potentially achieved, which corresponds to a high sensitivity of 178 nm per refractive index unit. Furthermore, FDTD modeling suggests that the electrochemically controlled tunability of plasmonic peaks is caused by reversible changes in the refractive index of the electrochromic polymer coating caused by oxidation or reduction reactions under external electrical potential. Consequently, we define the orthogonal plasmonic resonance shift as a shift that is orthogonal to the redox process responsible for the refractive index change. On the basis of these results, we suggest that the combination of anisotropic nanostructures and electrochromic matrix has the potential to reversibly electrically tune plasmonic resonances over the full visible spectrum.