Vallandigham died in 1871 in Lebanon, Ohio, at the age of 50, after accidentally shooting himself with a pistol. He was representing a defendant in a murder case for killing a man in a barroom brawl. Vallandigham attempted to prove the victim had in fact killed himself while trying to draw his pistol from a pocket when rising from a kneeling position. As Vallandigham conferred with fellow defense attorneys in his hotel room, he showed them how he would demonstrate this to the jury. Grabbing a pistol he believed to be unloaded, he put it in his pocket and enacted the events as they might have happened, shooting himself in the process. Vallandigham proved his point, and the defendant, Thomas McGehan, was acquitted and released from custody. Clement Vallandigham, however, died of his wound. His last words expressed his faith in "that good old Presbyterian doctrine of predestination". Survived by his wife, Louisa Anna (McMahon) Vallandingham, and his son Charles Vallandigham, he was buried in Woodland Cemetery, Dayton, Ohio.
Vallandigham was eulogized by James W. Wall, a former senator from New Jersey, who mentioned recently meeting with him about New Departure. Wall had been imprisoned during the Civil War by Union authorities.
John A. McMahon, Vallandigham's nephew, was also a U.S. Representative from Ohio.