Prior to the Civil War, Dreux had served as district attorney and a member of the Louisiana state legislature.
According to Grace King, those who knew him described him "as a man of great personal magnetism; brilliant, eloquent, dashing." He left for the battlefield as Lieutenant Colonel of the Louisiana Guard Battalion, in command of Dreux's (1st) Battalion, composed of the first five companies that volunteered from Louisiana.
Three months later, he died at Young's Mill (Warwick, Virginia, now Newport News, Virginia) while on a failed mission to capture Union officers who often ate breakfast at Smith's Farm.
His last words were "Steady, boys! Steady!”
30,000 mourners attended his funeral in New Orleans.