He was the son of Daniel De Leon, an early leader in the American Labor movement.
He was also active in the Labor Research Association during the 1960s, and was a regular contributor of articles and book reviews to its publication “Economic Notes.” De Leon also worked as a librarian and French instructor at Kittrell Junior College, a Historically Black College in North Carolina from 1965 to 1967.
[1][2] He was employed by the American Association for Labor Legislation as a field investigator, writer, and researcher, 1912-1920, while continuing to contribute to Socialist Labor Party of America (SLP) publications under the pseudonym, Braset Marteau, but became politically and personally estranged from his father and from the SLP and was expelled from the Party in 1918.
De Leon contributed to and helped to edit the Advance, the Amalgamated Clothing Workers of America's newspaper from 1919 to 1922.
He translated several works from French including The Brass Bell and The Sword of Honor by Eugene Sue and Patriotism and the Worker by Gustave Herve for publication by the SLP publishing house and the New York Labor News Company.