Cully earned a Ph.D. in history at the University of Illinois, and he was a lifelong educator, first as a teacher at the Punahou School in Hawaii, then at the University of Indiana, and finally as a professor and administrator at Sangamon State University, which is now part of the University of Illinois system. He headed the oral history office at Sangamon and later became director of the Lincoln Legal Papers project and adviser to the Lincoln Presidential Library. Serving as a director of many professional societies, Cully received numerous awards for his expertise in history.
He devoted many hours to serving his community, including Planned Parenthood, the Springfield schools desegregation project, the board of directors of Springfield Marine Bank, and as a trustee of the charitable fund of his uncle, Shelby Cullom Davis ’30.
Cully is survived by his wife, Ann Chapman Davis; five children; and eight grandchildren.