The development of lithium–sulfur (Li–S) batteries is of practical significance to meet the rapidly escalating demand for advanced energy storage technologies with long life and high-energy density. However, the dissolution and shuttling of the intermediate polysulfides (PS) initiates the loss of active sulfur and the poisoning of the lithium anode, leading to unsatisfactory cyclability and consequently hinders the commercialization of Li–S batteries. Herein, we develop a facile strategy to tame the PS dissolution and the shuttling effect in the Li–S system by introducing a modified polybenzimidazole (mPBI) with multiple functions. As a binder, the excellent mechanical property of mPBI endows the sulfur electrode with strong integrity and, therefore, results in high sulfur loading (7.2 mg cm−2), whereas the abundant chemical interaction between mPBI and PS affords efficient PS adsorption to inhibit sulfur loss and prolong battery life. As a functional agent for the separator, the mPBI builds a PS shield onto the separator to block PS’s migration to further suppress the PS shuttling. The dual actions of mPBI confer an excellent performance of 750 mAh g−1 (or 5.2 mAh cm−2) after 500 cycles at C/5 on the Li–S battery with an ultralow capacity fading rate of 0.08% per cycle.