At Gettysburg, his brigade went to the relief of Col. Strong Vincent's brigade on Little Round Top. His vanguard repelled a Confederate attack that had outflanked Vincent's right. Col. Patrick O'Rorke of the 140th New York Infantry was killed leading that counterattack. Elements of Weed's brigade helped move the guns of Lt. Charles E. Hazlett's Battery D, 5th United States Artillery to the top of the hill. Weed was mortally wounded in the chest (possibly by a sharpshooter hidden in Devil's Den) while standing near these guns. His last words were reported as "I would rather die here than that the rebels should gain an inch of this ground." Lt. Hazlett was killed trying to hear what Weed was saying. Command of the brigade fell to Col. Kenner Garrard of the 146th New York Infantry.