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Abstract This is the first report of molybdenum carbide‐based electrocatalyst for sulfur‐based sodium‐metal batteries. MoC/Mo₂C is in situ grown on nitrogen‐doped carbon nanotubes in parallel with formation of extensive nanoporosity. Sulfur impregnation (50 wt% S) results in unique triphasic architecture termed molybdenum carbide–porous carbon nanotubes host (MoC/Mo₂C@PCNT–S). Quasi‐solid‐state phase transformation to Na₂S is promoted in carbonate electrolyte, with in situ time‐resolved Raman, X‐ray photoelectron spectroscopy, and optical analyses demonstrating minimal soluble polysulfides. MoC/Mo₂C@PCNT–S cathodes deliver among the most promising rate performance characteristics in the literature, achieving 987 mAh g⁻¹at 1 A g⁻¹, 818 mAh g⁻¹at 3 A g⁻¹, and 621 mAh g⁻¹at 5 A g⁻¹. The cells deliver superior cycling stability, retaining 650 mAh g⁻¹after 1000 cycles at 1.5 A g⁻¹, corresponding to 0.028% capacity decay per cycle. High mass loading cathodes (64 wt% S, 12.7 mg cm⁻²) also show cycling stability. Density functional theory demonstrates that formation energy of Na₂S_x(1 ≤x ≤ 4) on surface of MoC/Mo₂C is significantly lowered compared to analogous redox in liquid. Strong binding of Na₂S_x(1 ≤x ≤ 4) on MoC/Mo₂C surfaces results from charge transfer between the sulfur and Mo sites on carbides’ surface.