In the 1930s, Biddle was appointed to a number of important governmental roles. In 1934 President Franklin D. Roosevelt nominated him to become Chairman of the National Labor Relations Board. On February 9, 1939, Roosevelt nominated Biddle to the United States Court of Appeals for the Third Circuit, to a seat vacated by Joseph Buffington. The United States Senate confirmed Biddle on February 28, 1939, and he received his commission on March 4, 1939. He served only one year in the role before resigning on January 22, 1940, to become the United States Solicitor General. This also turned out to be a short-lived position when Roosevelt nominated him to the position of Attorney General of the United States in 1941. During this time he also served as chief counsel to the Special Congressional Committee to Investigate the Tennessee Valley Authority, from 1938 to 1939, and as director of Immigration and Naturalization Service at the United States Department of Justice in 1940.