McWilliams served in the 11th Airborne Division of the United States Army from 1955-1961, after which he took his Masters and Ph.D. degrees at the University of California, Berkeley.
Recordings are available of his last class, American Political Thought since the Civil War, which was continued after his death by his daughter, Susan McWilliams Barndt, a Ph.D. candidate in the department of politics at Princeton University at the time and currently an associate professor of politics at Pomona College.