Incorporating light-responsive azobenzene into polyelectrolytes couples photoinduced changes in steric interactions and polarity to ionic conductivity. The reversible isomerization of an azobenzene moiety yields a 2–7 times change in the ion conductivity (σtrans > σcis) depending on the polymer composition. These trends cannot be explained by differences in the glass-transition temperatures of the polymers. Instead, UV–vis spectroscopy reveals a bathochromic shift in the π → π* transition of cis-poly(azobenzene) upon adding lithium bis(trifluoromethane)sulfonimide (LiTFSI) salt, suggesting that coordination of the cis isomer with Li+ is responsible for its lower conductivity. In summary, azobenzene is a simple and convenient functional unit to control the conductivity of polymeric materials using light.