In 1987, de Jongh was appointed as Commissioner of Finance by Governor Alexander A. Farrelly, his first government position and one that had once been held by his grandfather, Percy de Jongh. In addition to his primary responsibilities for financial administration, de Jongh served as Chairman of the Governing Board of the Virgin Islands Water and Power Authority and as an Executive Director and board member of the Virgin Islands Public Finance Authority. He was key in financial reforming and boosting the economy of the territory in the early 1990s. He also worked as an executive assistant to the governor's office, and he helped to coordinate better interagency cooperation. In 1992, he left government and returned to the private sector. That same year, de Jongh joined the real estate and insurance holding company, Lockhart Companies Incorporated where he served as President, CEO and a member of the board of directors until 2002. In 1993, he joined Public Financial Management, Inc., as a Senior Managing Consultant, where he helped to draft and implement Five-Year Plans for the cities of Philadelphia, Pennsylvania, New Haven, Connecticut, and Washington, D.C. From 1999-2001, de Jongh served as president of the St. Thomas-St. John Chamber of Commerce and headed a task force that created the Five Year Operating and Strategic Financial Plan for the government of the Virgin Islands, co-chaired a private-public sector group to negotiate with cruise lines and was selected as Rotary II's Person of the Year.