James Rodney Schlesinger was born in New York City on February 15, 1929. He attended Harvard University and earned a B.A. in 1950, an M.A. in 1952, and a Ph.D. in 1956, all in economics. He began teaching while he was pursuing his Ph.D. in 1955. He then taught economics at the University of Virginia until 1963. During his time as a professor, Schlesinger published his first book The Political Economy of National Security in 1960. 

In 1963, he moved to the Rand Corporation and eventually became the director of strategic studies for the think tank. In 1969, Schlesinger moved from the academic world to the realm of public service. That year, President Richard M. Nixon appointed Schlesinger as the assistant director of the Bureau of the Budget. After two years in that position, he was appointed chairman of the Atomic Energy Commission.

The Watergate scandal brought turmoil upon the Nixon Administration. In 1973, Nixon fired Richard Helms, who was the director of the Central Intelligence Agency (CIA), and replaced him with Schlesinger. Five months after being appointed director of the CIA, however, Schlesinger was replaced by William Colby, and Schlesinger moved over to the Pentagon as secretary of defense. Soon after his appointment, Schlesinger outlined his basic objectives. These included a "strong defense establishment;" "assure military balance so necessary to deterrence and a more enduring peace;" and to obtain for members of the military "the respect, dignity, and support that are their due." Schlesinger remained secretary of defense until November 1975 when Gerald Ford dismissed him. The two men disagreed on almost every issue, including détente with the Soviet Union and defense spending. Also Ford took issue with Schlesinger's abrupt style of dealing with his colleagues.

However, Schlesinger's public service career did not end in 1975. After Jimmy Carter won the election, he appointed Schlesinger as his special adviser on energy in January 1977. Nine months later, Schlesinger became the first head of the new Department of Energy; he held this position until July 1979. After Carter replaced him, Schlesinger became senior advisor to Lehman Brothers, Kuhn Loeb Inc., in New York.

He then continued his career in public service by serving on many government commissions and advisory groups. He served on the President's Commission on Strategic Forces (1982-1983) and was vice chairman of the President's Blue Ribbon Task Group on Nuclear Weapons Program Management (1984-1985). From 1999 to 2003, he was a member of the Panel to Assess the Reliability, Safety, and Security of the U.S. Nuclear Stockpile, and from 1998 to 2001 he was a member of the U.S. Commission on National Security/21st Century. He served as co-chair of Defense Science Board Task Force on the Future of the Global Positioning System. He was also a member of an independent team reviewing the Global Positioning System for the U.S. Air Force. In 1989, Schlesinger published his second book, America at Century's End, along with numerous articles.