Bloom briefly served in the U.S. Army during WWI. He became the associate pathologist at Michael Reese Hospital from 1923 to 1925. In 1926 Bloom came to the University of Chicago as the Smith Foundation Fellow in Anatomy. He became an Assistant Professor in 1929, Associate Professor in 1933, and Professor in 1941. He served as Chairman of the Department of Anatomy from 1941 to 1946, and in 1957 was names the Charles H. Swift Distinguished Service Professor in the Departments of Anatomy and in the Committee on Biophysics. Bloom became emeritus in 1965, retiring in 1969. Bloom was one of nine University of Chicago faculty to become one of the “Starred Men of Science” in 1944.