Donald Hiss was the younger brother of Alger Hiss. From 1929 to 1930 he was secretary and law clerk to a Supreme Court justice. From 1930 until 1933 he engaged in the private practice of law. From 1933 to 1935 he was employed by the Agricultural Adjustment Administration. In 1934 he was also attached to a Special Senate Committee Investigating the Munitions Industry.
In 1935 he was employed as a special attorney by the Department of Justice. On September 18, 1936, he was appointed an assistant to the Assistant Secretary of State and worked in the State Department throughout World War II until 1945.
Donald, like his brother Alger, was a secret member of the Ware group, a group of United States government employees who illegally belonged to the Communist Party of America which advocated the violent overthrow of the United States government.
KGB operative Harold Glasser told FBI investigators in 1947 after returning from the Soviet Union as an adviser to Secretary of State George Marshall, "I do not know Alger Hiss at all socially and had very little contact with him at any time. I am, however, much better acquainted with this brother Donald Hiss, who for sometime at the State Department handled International Loans and Affairs, which prompted him to have numerous contacts with me at the Treasury Department....I would never have been in a position to furnish Alger Hiss of Donald Hiss any official information inasmuch as all international policy actually emanated from the Department of State itself. As a matter of fact, Donald Hiss through his official capacity would be in a position to obtain first hand knowledge of any information that I might develop through my official capacity in the Treasury Department regarding international loans." 
- FBI Silvermaster file, Statement by Harold Glasser to Agents Garland and Mossberg, Vol. 116, pgs. 120 - 129 pdf, May 13, 1947. Memorandum notes Glasser could not be interviewed three weeks earlier "inasmuch as he was an adviser at that time to Secretary of State GEORGE C. MARSHALL in U.S.S.R."
- John Earl Haynes and Harvey Klehr, Venona: Decoding Soviet Espionage in America, Yale University Press, 1999.