Mims began his career at his alma mater, Vanderbilt University, where he became an assistant professor in 1892. One of his requirements was to ask his students to learn a thousand verses of poetry by heart. He wrote a history of Vanderbilt University as well as of Chancellor Kirkland. Stuart's
Beyond Dark Hills, was the direct result of one of Mims's assignments (writing an autobiographical essay); it was published in 1938. However, Allen Tate tried to expose his hypocrisy as Mims assured Ransom he would be welcome to stay in his department at Vanderbilt. Another colleague,
Lyle H. Lanier, agreed that this demonstrated Mims's hypocrisy. A progressive, Mims became vocal in his opposition to
lynching. He established the
Law and Order League, an anti-lynching organization. He also addressed the
New York Southern Society in
New York City, where he reiterated his opposition to lynching. His 1926 book entitled
The Advancing South was a call to action for progressives in the South. It was reviewed favourably by
Alain Leroy Locke (1885–1954) in
Opportunity: A Journal of Negro Life. Mims served as President of the Association of Colleges and Secondary Schools for Southern States, later known as the
Southern Association of Colleges and Schools, in 1902. He then served on its executive committee. He lectured at the
Chautauqua Institution in 1912-1942. He was also a member of the
Methodist Episcopal Church and served on the joint hymn book commission between the Methodist Episcopal Church, North and the
Methodist Episcopal Church, South in 1902-1903. ==Personal life, death and legacy==