Calvert Magruder (December 26, 1893 – May 22, 1968) was a Judge of the United States Court of Appeals for the First Circuit.
After attending Harvard Law School, Magruder served for one year as a law clerk to Justice Louis Brandeis of the Supreme Court of the United States. He became a law professor at Harvard Law School in 1920 and was Vice Dean of the school from 1929 to 1939. During the New Deal administration of President Franklin D. Roosevelt, Magruder served as General Counsel of the National Labor Relations Board from 1934 to 1935 and as General Counsel of the Wage and Hour Division of the United States Department of Labor from 1938 to 1939.
In 1939, President Roosevelt nominated Magruder to serve on the First Circuit. Magruder served as an active judge for twenty years, until 1959. Magruder also served as the Chief Judge of the First Circuit from 1948 until 1959. In addition to his service on the First Circuit, during World War II, Magruder also served as a judge of the United States Emergency Court of Appeals.
In 1959, Magruder took senior status, but continued to hear some cases until his death in 1968. His papers are archived at Harvard Law School and were a primary source for the book History of the United States Court of Appeals for the First Circuit by Professor George Dargo.