Although primarily a minister, Holmes helped found the National Association for the Advancement of Coloured People (NAACP) in 1909, and the American Civil Liberties Union (ACLU) in 1920, serving as its chairman from 1940 to 1950, after the resignation of Harry F. Ward.
Holmes, mainly a clergyman, was instrumental in establishing two influential organizations: the NAACP in 1909 and the ACLU in 1920. He headed the ACLU from 1940 to 1950 after Harry F. Ward stepped down.