Herein, an electrochemical hydrogen atom transfer (HAT) strategy for C(sp2)-H formylation of electron-deficient quinolines and isoquinolines is described. The cheap methanol acts as a formyl source with a catalytic amount of N-hydroxyphthalimide (NHPI) as the hydrogen atom transfer (HAT) catalyst. The advantages of this reaction are transition-metal-catalyst- and chemical-oxidant-free conditions, and the protocol could also be applied to the direct C(sp2)-H acetylation or propionylation of quinolines.