We demonstrate high-performance, flexible, transparent electrochromic (EC) films fabricated on an ITO/Ag/ITO (IAI) multilayer electrode prepared by roll-to-roll (RTR) sputtering. The IAI multilayer RTR sputtered on a polyethylene terephthalate (PET) substrate at room temperature exhibited a high optical transmittance of 82.4% and a very low sheet resistance of 8.93 Omega/sq. In addition, bending and cycling fatigue tests demonstrated better flexibility of the IAI multilayer than that of a sputtered ITO film. Poly(3-hexylthiophene) (P3HT) films prepared on IAI multilayers exhibited fast switching response between colored and bleached states, together with high reversibility and long-term stability of the EC behavior, which is comparable to the P3HT on a ITO/glass substrate. Moreover, after bending test, P3HT on IAI multilayer electrode also showed stable EC coloration, Based on the observed EC performance, the RTR sputtered IAI multilayer is proposed as an excellent substitute for conventional ITO film electrodes in order to realize large-area, transparent, flexible EC devices for flexible smart window applications.