 After his retirement as a civil servant he became chairman of the Holland Financial Centre, research fellow at the Netherlands School for Public Administration and chairman of the advisory board of IRS, a company active in the field of security, investigations and integrity management.Although at first a member of the social liberal D66, Doctors van Leeuwen became a member of the VVD, for which he co-authored the new foundational program, the "Liberal Manifest".In 2006, he was a candidate for the VVD for the Dutch general election.