Larson then worked as a lawyer for four years with the firm of Quarles, Spence and Quarles in Milwaukee, Wisconsin. When Depression-era conditions led to his layoff in the summer of 1939, Larson found a job as assistant professor of law at the University of Tennessee College of Law in Knoxville. While in Tennessee, he and Florence Newcomb Larson had two children. In 1941, during World War II, Larson moved to Washington, DC, when he mostly worked as a lumber industry regulator at the Office of Price Administration. In 1945, he became an assistant professor of law at Cornell Law School in Ithaca, New York. Over the next seven years, he produced a legal treatise on the Law of Workers' Compensation. The treatise is continually updated and is still used by lawyers and judges today. His son, Lex K. Larson, is the current editor. The treatise was the first publication to treat workers’ compensation as a distinct area of law with its own legal doctrines and rules for injured and deceased workers. It is currently 17 volumes in length. In 1953, Larson was appointed dean of the University of Pittsburgh School of Law in Pittsburgh, Pennsylvania.
Larson's status as an expert on the welfare state and his strong public speaking abilities led to appointment as Under Secretary of Labor in March 1954 in the Eisenhower administration. He supported a union shop to compel workers into a labor union as "a case of the individual... having to conform to the will of the majority." Larson soon became an articulate spokesman for Moderate Republicans. He declared himself part of "the American center" to which he also included President Eisenhower; Eisenhower's two-time opponent, Adlai Stevenson II; and Dean Acheson, a former secretary of state in the Harry Truman administration. Larson's most popular book, A Republican Looks at His Party was personally endorsed by Eisenhower. Eisenhower named Larson the director of the United States Information Agency in December 1956 and as his top speechwriter in October 1957.
He died in Durham on March 27, 1993. It is unknown if he was in his later years a registered Republican in North Carolina.
Legacy
Larson is criticized as a prototypical big government Republican in Barry Goldwater's landmark small government Republican manifesto, The Conscience of a Conservative. However, his life and work are treated at length in a biography by David Stebenne, Modern Republican: Arthur Larson and the Eisenhower Years.