From 1988 to 1993, Fleihan worked at the International Monetary Fund in Washington DC. He worked there as an advisor and then senior advisor to the Saudi executive director. He also worked at the United Nations Development Programme. In 1993, he left his job and returned to Lebanon, where he had been asked to assist in the post-war rehabilitation of the ministry of finance. While working as an adviser at the ministry, from 1993 to 1999, Fleihan also taught economics at his old alma mater, the American University of Beirut (AUB).