After World War II had begun, he was drafted into the Navy during his freshman year at Dartmouth and served on a destroyer in the Pacific. He returned to Dartmouth to graduate with a degree in government, after which he studied at the Institut d’Études Politiques de Paris. He then served in the Foreign Service in France and Greece. While working in Paris he met Adlai E. Stevenson, who became the Democratic Party’s presidential candidate in 1952 and 1956. Mr. Stevenson urged him to return to the United States and become involved in politics. From 1965 until his death, Mr. Hemenway was national director of the National Committee for an Effective Congress, which was founded in 1948 by Eleanor Roosevelt and others to support left-leaning candidates for Congress and the Democratic Party. By the 1976, its power had grown to the extent that the newspaper The National Observer called it “perhaps the most powerful political force in this country.” Mr. Hemenway, who also had a home in Manhattan, married Catherine Casey in 1951. She died in 1999. He is survived by their daughter, Anne Hemenway; his son from another relationship, Brent Hemenway; his sister, Joyce H. Brown; and two grandsons.