The chemical stability of alkaline polymer electrolytes (APEs) is paramount for ensuring the long-term durability of alkaline polyelectrolyte fuel cells. Convenient methods for acquiring highly stable polymers are pivotal for fuel cell commercialization. Herein, we propose a novel strategy involving post-polymerization and grafting via cross-metathesis reaction to yield highly alkaline-stable quaternary ammonium polynorbornenes (QAPNBs). This method boasts mild reaction conditions, high yields, and cost-effective reactants. The yields have increased from less than 40 % to an impressive 80 %. Upon comparing the alkaline stability of APEs with different side chain structures, it was observed that the presence of unsaturated double bonds in the side chain adversely affected the cations, while saturated APEs retained over 90 % of the cations during stability tests at 80 °C and 1 M KOH for 4800 h. Employing the QAPNBs in fuel cells resulted in a peak power density of 2.32 W cm−2 and a durability of 200 h at 600 mA cm−2.