Proton-conducting gel polymer electrolytes based on gelatin plasticized with glycerol and containing acetic acid were investigated, characterized, and applied to electrochromic window. For glycerol contents varying from 7% to 48%, the conductivity of the uniform and predominantly amorphous gel electrolyte was found to follow a Vogel-Tamman-Fulcher behavior with the temperature. Typically, for the electrolyte chosen to make 7×2 cm
2
electrochromic smart window with the configuration: glass/fluor-doped tin oxide (FTO)/WO
3
/gelatin electrolyte/CeO
2
-TiO
2
/FTO/glass and containing 28% of glycerol, the conductivities were found to be of the order of 5×10
−5
S/cm at room temperature and 3.6×10
−4
S/cm at 80°C. The device was characterized by spectroelectrochemical techniques and was tested up to 10,000 cycles showing a fast coloring/bleaching behavior, where the coloring process was achieved in 10 s and the bleaching in 2 s. The transmission variation at the wavelength of 550 nm was about 15%. The cyclic voltammograms showed a very good reversibility of the cathodic/anodic processes, and the charge density was about 3.5 mC/cm
2
. The memory tests showed that the transmittance in the colored state increased by 8% in 90 min after removing the potential.