Herein, we report a general and scalable continuous flow metallaphotoredox amidine arylation protocol that efficiently couples diverse (hetero)aryl halides and amidines under mild open-air conditions. Mechanistic studies revealed the pivotal role of an in situ generated triazine cocatalyst, which acts as the quencher in the photocatalytic cycle via an underexplored oxidative quenching pathway. Its strategic use as a cocatalyst enabled faster kinetics, broader nucleophile scope, including sulfonamides and amines, and the use of alternative solvents. These insights unlock a previously challenging reactivity, enhancing both the synthetic utility and sustainability of our nickel/photoredox cross-coupling.