With the appointment, the 54-year-old de Nysschen takes on oversight of sales, pricing and network development; strategic brand developmen; and marketing and product planning, including engineering and design.
He will replace Bill Peffer, who left in June after 10 months in the role.
Prior to accepting the new role, de Nysschen spent the past two years leading Nissan's Infiniti brand. Prior to that, he was the chief executive of Audi USA for eight years and president of Audi Japan for five years. He began his career with Audi in South Africa in 1993.
In 2013, the Cadillac XTS prestige luxury car was the brand's leading commercial fleet vehicle with 1,347 registrations.