Leonard James Arrington was born in 1917 on a farm near Twin Falls, Idaho, and spent his childhood and youth in an agricultural environment. After graduating from high school and the University of Idaho, he began graduate study in economics at the University of North Carolina. After military service in North Africa and Italy during World War II, he returned to complete a Ph.D. with a dissertation later published in 1958 as Great Basin Kingdom: An Economic History of the Latter-day Saints, 1830-1900. After marrying Grace Fort, Arrington accepted an appointment to teach economics at Utah State University. The couple had three children - James, Carl and Susan (Madsen). Both individually and in collaboration with students and other scholars, Arrington was incredibly prolific in producing historical articles and books. In 1965 he became the first president of the Mormon History Association. He also served as president of the Western History Association, the Agricultural History Society, and the Pacific Coast branch of the American History Association. In 1986 he was named a Fellow of the Society of American Historians.

He was appointed LDS Church Historian in 1972 (title later changed to Director of History Division). Simultaneously, he was Lemuel Redd Professor of History and director of the Charles Redd Center for Western Studies at Brigham Young University. For ten years he supervised a team of professional historians and researchers in producing significant scholarly work along the broad front of Mormon history: finding aids, task papers, oral histories, articles for popular audiences, biographies, and works of synthesis. His book The Mormon Experience: A History of the Latter-day Saints with Davis Bitton, published by Knopf in 1979, has been widely disseminated.

In 1982, when the LDS Church History Division was disbanded, most of its employees were transferred to the Joseph Fielding Smith Institute for Church History at Brigham Young University. Arrington served as director of this institute until his retirement in 1987. His book Brigham Young; American Moses won the prestigious Evans biography award.

Grace Fort Arrington died in 1982, and Arrington later married Harriet Ann Horne. Since his retirement he has continued to be active, producing under a history of Idaho in 1993 as well as other histories and biographies.