Graphitic carbon nitride g-C₃N₄ (GCN) has attracted extensive attention for electrochemical energy storage and conversion due to its high surface area, metal-free characteristics, “earth-abundance,” and facile synthesis. Furthermore, GCN has been demonstrated to exhibit a chemical interaction with polysulfides because of functional pyridinic nitrogen atoms, thus representing promising properties for application in lithium–sulfur (Li–S) batteries. Herein, an oxygen-doped hexagonal tubular carbon nitride (O-TCN) is obtained through a simple hydrolysis and pyrolysis approach. The tubular structure favors electrolyte infiltration and accommodates the volume change of sulfur during the redox reaction. Moreover, O-TCN/S with a high content of pyridinic N of about 80 wt% as the sulfur host is beneficial for trapping various polysulfide intermediates via numerous strong N–Li chemical interactions, further facilitating the transformation from high-order polysulfides to low-order Li₂S₂ or Li₂S. As a result, O-TCN delivers a high discharge capacity of 1281 mAh·g⁻¹ at 0.05 C for the first cycle, and an excellent reversible capacity of 401 mAh g⁻¹ after 1000 cycles at 0.5 C with an ultralow capacity decay of 0.064% per cycle, presenting a high sulfur utilization and capacity retention.