Graphitic carbon nitride (g-C 3 N 4 ) with pronounced excitation of lone pairs benefits from extended visible light absorption, which thus enhances its photocatalytic hydrogen (H 2 ) generation activity. However, achieving such lone pair excitation in g-C 3 N 4 remains a grand challenge. Here we report on the synthesis of g-C 3 N 4 with remarkable lone pair excitation through thermolysis of protonated melamine via a facile microwave-assisted heating. The g-C 3 N 4 photocatalyst after optimizing the proton concentration offers a highest H 2 generation rate of 21.4 μmol h −1 , which is nearly 7 times higher than that of g-C 3 N 4 created from unprotonated melamine under identical conditions (3.2 μmol h −1 ). Furthermore, active H 2 generation at 490 nm light irradiation (2.3 μmol h −1 ) is realized owing to the lone pair excitation. This work shows the great potential of protonation combined with microwave-assisted heating for activating the lone pair excitation in g-C 3 N 4 for increased photocatalytic performance. Graphitic carbon nitride (g-C 3 N 4 ) with pronounced excitation of lone pairs enhances its photocatalytic hydrogen (H 2 ) generation activity.