A new monomer called 2,2′‐(4,4′‐oxydiphenol‐4,4′‐diyl)bis(2‐methyl‐2,3,3a,4,7,7a‐hexahydro‐1H‐4,7‐methanoisoindol‐2‐ium) iodide (d3) is synthesized possessing both cross‐linker and functional groups. The membranes are formed by copolymerizing d3 with norbornene and (3aR,4S,7R,7aS)‐2‐methyl‐2‐(3‐(trimethylammonio)propyl)‐2,3,3a,4,7,7a‐hexahydro‐1H‐4,7‐methanoisoindol‐2‐ium iodide (a3) at varying ratios. The water uptake is 41.35% at 60 °C, and ion exchange capacity is 2.35 mequiv g−1 for a mole ratio of a3, norbornene, and d3 (1:6:3). The conductivity is 12, 37, and 40 mS cm−1 when d3 is decreased. Meanwhile, the conductivity increases quickly with increasing the temperature. Furthermore, the mechanical properties and thermal properties are improved, attributed to the increased cross‐linker. The membrane has a tensile strength of 41.3 MPa and the elongation at break of 38.0 %, and the 5 wt% loss temperature for membrane is ≈159 °C. The H2/O2 single fuel cells with this membrane show a maximum power density of 124 mW cm−2 at 50 °C. The cross‐linked membranes demonstrate high‐dimensional stability in alkaline solution.