 A novel carbon material for use in lithium–sulfur batteries is fabricated from the seaweed Enteromorpha prolifera, a renewable source that grows rapidly in the sea near Qingdao, China, during the summer. The E. prolifera-derived carbon (EPC) possesses a multilevel micropore–mesopore structure and a certain amount of oxygen- and nitrogen-containing functional groups. In addition, the hierarchical porous carbon also possesses a high specific surface area of 3536.58 m2 g−1 and a large pore volume of 1.754 cm3 g−1. The carbon can thus be loaded with a high sulfur content (EPC/S, 74.8 wt%), making it a promising candidate for use as the cathode material in lithium–sulfur batteries. The EPC was characterized using field-emission scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, the Brunauer–Emmett–Teller method, and other methods. The EPC/S cathode exhibited superior electrochemical performance; the first discharge capacity was as high as 1328 mA h g−1 at 0.1 C. Further, the capacity was 520 mA h g−1 after 100 cycles at 0.5 C and 510 mA h g−1 after 100 cycles at 1 C.