A one-pot, hydrothermal synthesis of nitrogen and sulfur dual doped carbon aerogels is presented, derived from our previously published hydrothermal carbonization approach. Two co-monomers, S-(2-thienyl)-L-cysteine (TC) and 2-thienyl carboxaldehyde (TCA), were used for sulfur incorporation, giving rise to distinct morphologies and varying doping levels of sulfur. Nitrogen-doping levels of 5 wt% and sulfur-doping levels of 1 wt% (using TCA) to 4 wt% (using TC) were obtained. A secondary pyrolysis step was used to further tune the carbon aerogel conductivity and heteroatom binding states. By comparing solely nitrogen-doped with nitrogen- and sulfur-doped carbon aerogels, it was observed that the presence of sulfur improves the overall electrocatalytic activity of the carbon material in both basic and acidic media. This study of the synergistic effect of combined sulfur- and nitrogen-doping in the catalysis of the “oxygen reduction reaction” (ORR) is expected to be significant to future research concerning the improvement of heterogeneous, metal-free, carbon-based catalysts.