Donald Hiss's name was mentioned during the 1948 hearings wherein his more famous and older brother, Alger, was accused of spying for the Soviet Union, and two years later convicted of perjury before the House Un-American Activities Committee (HUAC).

[4] In 1932, he was a law secretary to Associate Justice Oliver Wendell Holmes of the United States Supreme Court.

[5] On August 3, 1948, Whittaker Chambers included the name of Donald Hiss along with his brother Alger and more than half a dozen other former Federal officials as members of the Ware Group and of the Communist Party when testifying under subpoena to HUAC.

Cox was famous as Thurman Arnold's chief deputy," as an early partner at Root Clark & Bird[8] (later Root, Clark, Buckner & Ballantine; later Dewey Ballantine, later Dewey & LeBoeuf) and fellow attorney with Hiss at Covington & Burling, where he was called the "perfect advocate"[9]) during the Hiss-Chambers Case.

[5][13][14] Donald Hiss spent the remainder of his career in private law practice with Covington & Burling.

[5][13][15] Dean Acheson, who famously defended the reputation of Alger Hiss, was also a member of Covington & Burling.