As an intellectual, Harrison was an unrivaled soapbox orator, a featured lecturer for the New York City Board of Education's prestigious "Trend of the Times" series, a prolific and influential writer, and, reportedly, the first Black person to write regularly published book reviews in history. His efforts in these areas were lauded by both black and white writers, intellectuals, and activists such as Eugene O'Neill, James Weldon Johnson, Henry Miller, Hermie Huiswoud, William Pickens, Bertha Howe, Hodge Kirnon, and Oscar Benson. Harrison aided Black writers and artists, including Charles Gilpin, Andy Razaf, J. A. Rogers, Eubie Blake, Walter Everette Hawkins, Claude McKay, Solomon Tshekisho Plaatje, Lucian B. Watkins, and Augusta Savage. He was a pioneer Black participant in the freethought and birth control movements as well as being a bibliophile and library popularizer. He created "Poetry for the People" columns in various publications, including the "New Negro" magazine (1919), Garvey's "Negro World" (1920), and the International Colored Unity League's "The Voice of the Negro" (1927).