Lithium-sulfur (Li-S) batteries have garnered significant interest as a strong contender for future energy storage, characterized by their remarkable energy density and cost-effectiveness. However, the sluggish conversion kinetics of the polysulfide intermediates, compounded with their shuttling behaviors, pose considerable challenges in sulfur electrochemistry. Herein, we develop a novel iron monoboride (FeB) electrocatalyst for boosting sulfur reactions and enhancing Li-S battery performance. The ultrafine powdery FeB affords abundant and fully exposed active interfaces for host-guest interactions. Meanwhile, the intrinsic high conductivity of FeB, combined with its strong adsorption and catalytic activity to polysulfides, enables substantial inhibition of the shuttle effect and enhancement of conversion kinetics. As a result, sulfur electrodes equipped with the FeB nanocatalyst realize excellent cyclability with a minimal capacity fading of 0.04 % per cycle over 500 cycles, as well as favorable rate capability up to 7 C. Moreover, decent areal capacity and cycling stability can be also achieved under high-loading (5.1 mg cm-2) and limited-electrolyte (7.0 mL g-1) configurations. This study presents a facile approach and insightful perspective on nanostructured metal boride for highly efficient sulfur electrocatalysis, holding good promise for the advancement of high-performance Li-S batteries.