In lithium–sulfur (Li–S) batteries, the impregnation of sulfur into electrically conductive materials of porous carbon plays a significant role in preventing the dissolution of lithium polysulfide (LiPS) into an electrolyte solution and improving cycling performance. However, this strategy does not render high-energy density to Li–S cells because of the limited amount of sulfur in porous carbon. Once the sulfur overflows out of porous carbon because of the significant volume change occurring during charge–discharge cycling, the LiPS formed outside porous carbon probably diffuses toward the anode, leading to poor cycling performance. In this study, the poly-2-acrylamido-2-methylpropanesulfonic acid (AMPS)-based polymer incorporated into the sulfur/porous carbon composite cathode in a Li–S cell effectively suppresses LiPS dissolution even when sulfur is present outside porous carbon, achieving good cycling performance with a capacity retention of 72% at the 100th cycle. Herein, the polymer used is poly-AMPS with a crosslinker of N-[tris(3-acrylamidopropoxymethyl)methyl]acrylamide, which is synthesized using 2-hydroxy-2-methylpropiophenone as the photoinitiator. The characteristics of the as-synthesized AMPS-based polymer and sulfur–carbon composite cathode are meticulously investigated by scanning electron microscopy–energy-dispersive X-ray spectrometry, transmission electron microscopy, dynamic light-scattering analysis, thermogravimetric analysis, and X-ray diffraction.