Farwell graduated from Ohio State University and the University of Chicago (M.A., 1968). He served in World War II as a captain of engineers attached to the Mediterranean Allied Air Force in the British Eighth Army area and later also saw combat in the Korean War. He separated from the military after seven years of active duty.
As a civilian, he became director of public relations and director of administration for Chrysler International from 1959 to 1971. He also served three terms as mayor of Hillsboro, Virginia (1977-81).
He published articles in the New York Times, Washington Post, American Heritage, Harper's, Horizon, Smithsonian Magazine as well as serving as a contributing editor to Military History, World War II, and Collier's Encyclopedia. Farwell also published biographies of Stonewall Jackson, Henry M. Stanley, and Sir Richard Francis Burton.
He was a fellow of the MacDowell Colony and a member of both the Royal Geographical Society and the Royal Society of Literature.
Farwell gave his papers to the University of Iowa.