Although many redox-active organic compounds have been developed, how to improve stability and solubility remains to be a challenge in the development of organic redox flow batteries (RFBs). Furthermore, the crossover of organic redox electrolytes and limited types of membranes present additional challenges to examine the long-term cyclability of these materials in nonaqueous RFBs. To overcome these limitations, we developed a new type of pyridinium-based negolytes. The π-conjugation of the pyridinium core was extended by introducing 1,3-azoles into the C4-position of pyridinium by Pd-catalyzed C–H arylation, which revealed the superiority of benzothiazole as a stabilizing group. In addition, cationic quaternary ammonium functional groups at the N-substituent decreased the crossover of the pyridinium negolytes through an anion exchange membrane. Moreover, the solubility of the negolyte was increased by using bis(trifluoromethanesulfonyl)imide (TFSI) as a counteranion. A 0.1 M solution of the dicationic benzothiazolylpyridinium exhibited 0.0083% capacity-fading rate per cycle in symmetric RFBs for 250 cycles and 0.08% in full RFBs containing the ammonium-substituted ferrocene as a posolyte for 500 cycles. The heteroarylpyridinium scaffold and the combined strategies to address stability, solubility, and crossover issues will promote further development of nonaqueous organic RFBs.