Judd, a Nebraskan, served in the U.S. Armed forces in World War I. After medical school at the University of Nebraska, he went to China in 1925 under the American Board of Commissioners for Foreign Missions. He served in a mission hospital in Fukien (Fujian) Province (1926-1931). Frequent bouts of malaria forced him to return for a time to the United States, but he was back to China in 1934 to direct a mission hospital in Fenchow (Fenzhou), Shansi (Shanxi) Province, He lived under Japanese occupation for several months in late 1937 and 1938 before returning again to the United States, where between 1938 and 1940 he made over 1,400 speeches warning of Japanese aggression.
After World War II, as a U.S. congressman from Minnesota (1943-1962), Judd was an eloquent and vigorous defender of Nationalist China, playing an important role in U. S. Far Eastern policy. No U.S. former China missionary ever served in so high an elected office. He promoted overseas recovery programs. At the 1960 Republican National Convention he gave a rousing keynote address and nearly received the vice-presidential nomination. He was defeated in his Congressional reelection bid in 1962.