Clark became a professor at the University of Kentucky in 1931. With few resources at his disposal, he almost single-handedly built Kentucky's history department into a major doctoral program in southern history. At one point its star-studded faculty included Albert D. Kirwan, Clement Eaton, James F. Hopkins, Holman Hamilton, Steven A. Channing, and Charles P. Roland. Clark began a 70-year-long enterprise at cataloging, organizing, rescuing, and preserving Kentucky's history. He established at UK a culture of respect for the heritage and documentation of the past. He re-organized the History department, bringing revolutionary innovations to the way the subject was researched and taught. His comprehensive methods were inclusive and exhaustive in scope and detail yet presented to his students in a logical and eloquent manner.