Lithium–sulfur batteries are attracting great attention due to their high theoretical capacity, low cost and environmental friendliness. However, the severe lithium polysulfides shuttling, self-discharge behavior and insulating end redox products (Li2S/Li2S2) remarkably hinder the performance. The cell configuration with an interlayer toward the cathode is an effective strategy to circumvent the above challenges. In this study, a carbon fibers/Ti3C2Tx interlayer is proposed to provide a physical shield and a strong chemical affinity to mitigate the polysulfides shuttling. The 3D cross-linked conductive networks of carbon fibers/Ti3C2Tx interlayers provide fast electron transfer channels and, thus, increase sulfur utilization and save “dead” sulfur. The dual effects of carbon fibers/Ti3C2Tx layers enable the Li–S cells with a high initial discharge capacity of 1380 mAhg−1 at a current density of 0.1 C and an ultralow capacity loss of 0.044% per cycle within 1000 cycles at 1 C. We found that the family of MXenes plays unique roles in immobilizing and converting the polysulfides. The design of a carbon fibers/Ti3C2Tx interlayer with dual effects paves the ways for improving the performance of battery systems that involve complex phase conversion reactions.