We developed a novel route to realize non-volatile, all-solid-state smart windows for on-demand infrared shielding, which enables us to intelligently regulate and utilize sunlight, leading to a solution for energy saving technology. Protonation of transition metal oxides (TMOs) is the most ideal route to regulate the transmission of sunlight because it reversibly changes electro-optical properties of a TMO. However, protonation of TMOs is not utilized for all-solid-state devices because it requires electrochemical reaction in a “liquid” electrolyte, which causes liquid leakage problem. In order to overcome this protonation issue, we used water-incorporated nanoporous glass as a “solid” electrolyte. We fabricated all-solid-state thin-film transistor (TFT) structure on a thermochromic TMO, vanadium dioxide (VO₂), films using a water-infiltrated nanoporous glass. As a consequence, we found that water electrolysis and protonation / deprotonation of VO₂ film surface occurred during gate voltage application, leading to reversible metal-insulator conversion of ~10-nm-thick VO₂ layer. This promising result can provide a novel route for TMO-based solid-state electro-optical devices, in particular, smart windows for on-demand infrared shielding.