An in situ sulfur deposition route has been developed for synthesizing sulfur–carbon composites as cathode materials for lithium–sulfur batteries. This facile synthesis method involves the precipitation of elemental sulfur into the nanopores of conductive carbon black (CCB). The microstructure and morphology of the composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that most of the sulfur in the amorphous phase is chemically well-dispersed in the nanopores of the CCB. The sulfur content in the composites is confirmed using thermogravimetry analysis (TGA). The S–CCB composites with different sulfur content (52 wt%, 56 wt% and 62 wt%) deliver remarkably high initial capacities of up to 1534.6, 1357.4 and 1185.9 mA h g−1 at the current density of 160 mA g−1, respectively. Correspondingly, they maintain stable capacities of 1012.2, 957.9 and 798.6 mA h g−1 with the capacity retention of over 75.1% after 100 cycles, exhibiting excellent cycle stability. The electrochemical reaction mechanism for the lithium–sulfur batteries during the discharge process is investigated by electrochemical impedance spectroscopy (EIS). The significantly improved electrochemical performance of the S–CCB composite is attributed to the carbon-wrapped sulfur structure, which suppresses the loss of active material during charging–discharging and the restrained migration of the polysulfide ions to the anode. This facile in situ sulfur deposition method represents a low-cost approach to obtain high performance sulfur–carbon composite cathodes for rechargeable lithium–sulfur batteries.