Prior to joining the World Bank, Ian Johnson, a British national, received a Bachelor of Science from the University of Wales and Masters' degrees from the University of Sussex and Harvard University. He subsequently spent five years in Bangladesh as a Program Officer for UNICEF working on rural development issues and one year as an economist in the British Government.

Johnson began his employment with the World Bank in 1980 as a Young Professional. In 1981 he joined the Europe, Middle East and North Africa (EMENA) Projects Department, Power and Energy Division (EMPPE) as an energy economist; he was subsequently promoted to Senior Economist. In 1987 he transferred to the EMENA Regional Office of the Vice President.

In April 1990, Johnson was named the Principal Sector Economist in the Policy, Research, and External Affairs Department (PRE). In April 1991, he became the Administrator of the newly created Global Environment Facility (GEF) where he played a key role in the structuring and first replenishment of the GEF. In September 1995, he was promoted to the position of Assistant Chief Executive Officer in the GEF Secretariat.

In 1997, Johnson was named the Senior Manager of the Environment Department and in 1998 he became the Vice President for Environmentally and Socially Sustainable Development (ESSD). On July 7, 2000, Johnson succeeded Ismail Serageldin as the Chairman of the Consultative Group on International Agricultural Research (CGIAR).

Johnson left the World Bank in 2006. He has subsequently served in various positions: as an advisor to the government of Chile; a member of the Swedish Commission on Climate Change and Development; as senior advisor to Global Legislators Organisation for a Balanced Environment (GLOBE) and chair of its Ecosystems Services Panel; as consultant to a number of other international organizations; and, beginning in 2010, as Secretary General of the Club of Rome.