In this study, for the first time an electrochemiluminescence sensor for ultra‐trace monitoring of lamotrigine is reported. The sensing probe was fabricated using silver prussian blue analogue as a new effective co‐reaction accelerator and carboxylated sulfur‐doped graphitic carbon nitride nanocomposite as a new green luminophore. Also potassium peroxydisulfate was utilized as a strong co‐reactant. The proposed ECL sensor exhibited excellent wide linear range (3.45×10−15 to 2.98×10−8 M), low detection limit (4.89×10−16 M), the relative standard deviation of 1.07 %, outstanding reproducibility and superior long‐term stability. The prominent advantages of the sensor showed that it can be used to determine LMT in clinical samples.