Johnson served as Deputy Assistant Secretary (1981–1982) and Assistant Secretary of the Treasury for Economic Policy (1982–1986). While at the Treasury, Johnson was responsible for the formulation of economic policy initiatives and development of the Administration's economic forecast for the budget. He was also instrumental in designing the Economic Recovery Tax Act of 1981 and the Tax Reform Act of 1986, which represents the most comprehensive change in the history of U.S. tax law. His performance at the Treasury won him the Alexander Hamilton Award, the department's highest honor.