Highly fluorescent nitrogen-doped graphitic carbon dots (NGCDs) are developed as new label-free chemosensors for gallium ion (Ga³⁺) detection for the first time. Through the pyrolysis of ammonium citrate in air, NGCDs have been prepared with high fluorescence quantum yield (FLQY: 44.8%). As-prepared NGCDs exhibit excellent photostability under continuous UV irradiation. Owing to the strong interaction between Ga³⁺ and the oxygen functional groups (e.g., hydroxyl, carboxyl), the fluorescent NGCDs chemosensor shows a highly sensitive and selective response (a detection limit of 209 nM) to Ga³⁺ in a wide concentration range of 0–20 μM. Further fluorescence lifetime analyses suggest the quenching mechanism appears to be a dynamic process.