Jordan's teaching career began in 1955 as a history instructor at
Phillips Exeter Academy. After completing graduate school, Jordan spent two years as a fellow at the
College of William and Mary's Institute of Early American History and Culture. He was Professor of History at
University of California, Berkeley, from 1963 to 1982, and the school's Associate Dean for Minority Group Affairs Graduate Division, 1968–70. As early as 1962, when he published an article on the status of '
mulattoes' in the
Thirteen Colonies, Jordan's work helped to illuminate the so-called
one-drop rule, a uniquely American example of
hypodescent. It defined as "black" or African-American, persons with any amount of
African ancestry, and was adopted into twentieth-century U.S. state laws, such as in 1924 in
Virginia. His synthesis,
White Over Black, looked at the history of race relations in the United States, and was influential for its assessment of issues of interracial sexuality. In assessing allegations about
Thomas Jefferson and a liaison with his slave, Jordan was the first historian to use
Dumas Malone's timeline of Jefferson's activities to demonstrate that he was at Monticello for the conception of each of Sally Hemings' children. In 1982, Jordan relocated to the
University of Mississippi, where he was the
William F. Winter Professor of History and Afro-American Studies for more than 20 years. While there he influenced many graduate and undergraduate students. ==Marriage and family==