Born in Allendale, South Carolina in 1897, Lewis K. McMillan did not attend school until he was eleven years old. He received his primary education from the Voorhees Institute and attended Benedict College for eighth and ninth grade. He finished his secondary schooling in Washington, DC. McMillan earned his bachelor of arts degree from Howard University, his bachelor of divinity degree from Yale, and his PhD in history and philosophy from the University of Bonn. Further graduate work was completed at the University of Pennsylvania, Ohio State University, and the University of Wisconsin. After graduating from Howard in 1922, McMillan worked as a southern regional field secretary for the YMCA and a reporter for the Afro-American newspaper of Baltimore. McMillan earned his BD from Yale in 1925. From 1929 to 1933, he studied in France and Germany.
After earning his doctorate in 1933, McMillan was a professor at Shaw University, Virginia State, and Bishop College in Texas. From 1935 to 1945, he served on the faculty of Wilberforce University. In 1947, McMillan went to South Carolina State College, where he was the first full-time faculty member to hold a doctorate. He taught history and, occasionally, German. In 1953, McMillan was fired for publishing a work critical of Black institutions in the state of South Carolina. His self-published Negro Higher Education in the State of South Carolina detailed the poor resources, lack of funding, and administration of the institutions. McMillan was especially critical of how Black faculty members were excluded from policy- and decision-making.
Although McMillan appealed his termination to the American Association of University Professors, the American Civil Liberties Union, and Southern Association of Colleges and Schools, he was not reinstated at South Carolina State. He also found himself shut out of opportunities at other Black colleges. He eventually returned with his family to Connecticut, where he taught at Bullard-Havens Technical High School, the University of Hartford, and the University of Bridgeport. From 1963 to 1965, he served on the Stratford Board of Education. He was a member of the Connecticut Safety Commission from 1963 to 1970. He was a Baptist minister and served churches in Connecticut on an interim basis at various points in his life.
In addition to his book, McMillan authored articles in academic journals on race and education. He undertook special newspaper assignments in Palestine in 1939 and in Germany in 1949. After moving to Connecticut, McMillan wrote a series of articles in 1954 for the Hartford Courant on school segregation. In 1967, he traveled to Germany and lectured at the University of Berlin and elsewhere. He wrote a series of articles about his experience, which were published in Connecticut newspapers. McMillan died in Stratford in 1974.