He was a law clerk for Associate Justice Louis Brandeis of the Supreme Court of the United States from 1916 to 1917.

He served as an infantry lieutenant in the United States Army from 1917 to 1919, during World War I.

He was general counsel for the Wage and Hour Division of the United States Department of Labor from 1938 to 1939.

[2] Magruder was nominated by President Franklin D. Roosevelt on April 24, 1939, to a seat on the United States Court of Appeals for the First Circuit vacated by Judge George Hutchins Bingham.

He died at the age of 74 and was living in Newton, Massachusetts, at the time of his death.