Solid polymer electrolytes offer improved safety over conventional liquid electrolytes but typically suffer from poor conductivity and cyclability. Here, two novel sulfur-containing polymers, cross-linked and block, were designed and synthesized using the thiol–ene click reaction then formulated into solid electrolytes and tested. The cross-linked polymer with succinonitrile and lithium salt incorporated demonstrated conductivity of up to 10^–4 S cm^–1 at 20 °C. The block polymer prepared by the sequential polymerization of a hard and conducting block demonstrated conductivity of up to 10^–5 S cm^–1 at 20 °C when combined with lithium salt. To make a full cell, the block polymer was mixed into the electrode whereas the cross-linked film was used as the combined solid polymer electrolyte and separator layer. At room temperature, the resulting cells achieved 200 cycles at a 0.05 C-rate with 72% capacity retention and over 3000 cycles at a 0.5 C-rate with greater than 90% capacity retention. The high performance of these cells, their ease of fabrication, and the prospects for future performance increases mark a significant advancement toward next-generation solid-state batteries operating at room temperature.