Leffler is the Edward R. Stettinius Professor of History at U.Va. He joined the faculty in 1986, after teaching at Vanderbilt, and chaired U.Va.'s Corcoran Department of History from 1990 to 1995. One of the country's leading authorities on modern U.S. foreign relations, he won the Bancroft Prize for his book A Preponderance of Power in 1993.
Leffler was a senior fellow at the Nobel Peace Institute in Oslo during 1993 and 1998, where he lectured on the Cold War. He served as president of the Society of Historians of American Foreign Relations in 1994.
In 1990, he was a member of the U.S. delegation to a joint Soviet-American symposium on the Cold War in Moscow and Washington. He served in the office of the Secretary of Defense during the Carter years, where he worked on arms control, confidence-building measures, and contingency planning as a fellow of the Council on Foreign Relations.