For the development of all‐solid‐state lithium metal batteries (LMBs), a high‐porous silica aerogel (SA)‐reinforced single‐Li+ conducting nanocomposite polymer electrolyte (NPE) is prepared via two‐step selective functionalization. The mesoporous SA is introduced as a mechanical framework for NPE as well as a channel for fast lithium cation migration. Two types of monomers containing weak‐binding imide anions and Li+ cations are synthesized and used to prepare NPEs, where these monomers are grafted in SA to produce SA‐based NPEs (SANPEs) as ionomer‐in‐framework. This hybrid SANPE exhibits high ionic conductivities (≈10−3 S cm−1), high modulus (≈105 Pa), high lithium transference number (0.84), and wide electrochemical window (>4.8 V). The resultant SANPE in the lithium symmetric cell possesses long‐term cyclic stability without short‐circuiting over 800 h under 0.2 mA cm−2. Furthermore, the LiFePO4|SANPE|Li solid‐state batteries present a high discharge capacity of 167 mAh g−1 at 0.1 C, good rate capability up to 1 C, wide operating temperatures (from −10 to 40 °C), and a stable cycling performance with 97% capacity retention and 100% coulombic efficiency after 75 cycles at 1 C and 25 °C. The SANPE demonstrates a new design principle for solid‐state electrolytes, allowing for a perfect complex between inorganic silica and organic polymer, for high‐energy‐density LMBs. High‐porous silica aeogel (SA)‐reinforced single‐Li+ conducting nanocomposite polymer electrolyte (NPE) is prepared using a series of single‐Li+ monomers (LiA, LiMTFSI, and LiSTFSI). The SA‐integrated single‐lithium conducting NPEs (SANPEs) exhibit high ionic conductivity, high lithium transference number, and a wide electrochemical window. Furthermore, the SANPE‐based lithium metal battery (LMB) shows the capability of suppressing Li dendrite growth.