All business activities were handed over to ISM eCompany (Innovative Solutions in Media) in 1997, the company of which De Jager was CEO until his appointment to the cabinet on 22 February 2010.

Besides his work as managing partner of the Rotterdam internet agency ISM eCompany (which he co-founded in 1992) and Sana Commerce (B2B e-commerce software) from 2008, De Jager is socially involved in different activities.

De Jager advocated by the Dutch contribution to the need to improve monitoring in a more prominent role of the International Monetary Fund and World Bank.

On 23 February 2010 following the resignation of Wouter Bos, and with him all the Labour Party members from the Fourth Balkenende cabinet, De Jager became Minister of Finance.

On 26 February 2012 former Minister of Finance Onno Ruding told journalist and television host Eva Jinek he had regular contact with De Jager on specific topics.