Born in London, Jackman was educated in New York City public schools, where in high school he began a lifetime friendship with Countee Cullen. Harold Jackman received a B.A. degree from New York University in 1923 and subsequently received a master's degree from Columbia University.
Rumored lover of Countee Cullen - two months after the latter's marriage, they sailed for Europe alone, without Cullen's bride.
A dedicated teacher, Jackman taught social studies for thirty years in the New York Public Schools system. He was active in many organizations including the Alpha Phi Alpha Fraternity, the NAACP, National Urban League, American Society of African Culture, and the Ira Aldridge Society. He was a life member and served on the executive board of the Negro Actors Guild.
He was also a contributing editor to Phylon from 1944-1956 and an advisory editor from 1957-1961. Jackman was a strong advocate for the arts and was a constant source of support for African American artists, encouraging them and promoting their careers.
Jackman was a friend of Carl Van Vechten, New York arts critic, novelist, photographer, and arts patron. He helped Van Vechten to build the James Weldon Johnson Memorial Collection of Negro Arts and Letters at Yale University, making donations and asking others to do so. At the encouragement of a friend, Jackman decided to establish a similar documentation program at Atlanta University.
Gleaning materials from his personal library, the Harold Jackman Collection of Contemporary Negro Life was established. Jackman continued to build the collection by acquiring materials through gifts and purchases and encouraging others including the artists themselves, to donate materials. In 1946, Jackman requested the collection be renamed the Countee Cullen Memorial Collection in honor of the noted Harlem Renaissance poet.
At the death of Harold Jackman, his sister Ivie Jackman formed the Harold Jackman Memorial Committee to carry on his work. Subsequently, the collection was renamed to honor both Cullen and Jackman.