After his dissertation on dealing with the impact of sea-level changes in the Caribbean, Herweijer lectured for two years in Utrecht before starting his career within General Electric (USA). At General Electric he received his management education while being exposed to various business roles and responsibilities. He joined IBM Global Network Services as manager of Sales Support for Europe, Middle-East, and Africa, followed by operational management in Banking, Insurance, Government, and Education in the Netherlands. During this period he was being schooled for executive management. Akzo (now Akzo Nobel) asked him to be the general manager of their information technology consulting and products business unit and later appointed him as their corporate officer of information systems. After successfully streamlining the European IT operations of Akzo, he became member of the Groepsraad of Getronics, where he was responsible for software and consulting, disaster recovery, and payment systems services. This was later followed by an appointment as board member of Origin International. Thereafter, he was for several years senior vice president for information systems and technology with Royal Ahold.