In his first decade in New York, Harrison started writing letters to the editor of "The New York Times" on topics such as lynching, Charles Darwin's theory of Evolution and literary criticism. He also began lecturing on such subjects as the poetry of Paul Laurence Dunbar and Reconstruction. As part of his civic efforts, Harrison worked with St. Benedict's Lyceum (along with bibliophile Arthur Schomburg from Puerto Rico, journalist John E. Bruce, and activist Samuel Duncan); St. Mark's Lyceum (with bibliophile George Young, educator/activist John Dotha Jones, and actor/activist Charles Burroughs); the White Rose Home (with educator/activist Frances Reynolds Keyser), and the Colored YMCA.