His father, Adam Opel, founded the Opel firm as a manufacturer of sewing machines, then expanded into bicycle manufacturing. After Adam's death in 1895, control of the company passed to his five sons. In 1898, Wilhelm and his brother Fritz brought Opel into the automobile industry with the purchase of the small Lutzmann automobile factory of Dessau.
Along with his brother Heinrich, Wilhelm was raised to grand-ducal nobility in 1917. Their brother Karl was raised to the same level in the next year.