Public Law 81-36, 2 April 1949, originally established this position as the Under Secretary of Defense, however Public Law 81-2 16, August 10, 1949, a.k.a. the 1949 Amendments to the National Security Act of 1947, changed the title to Deputy Secretary of Defense.
Public Law 92-596, October 27, 1972, established a Second Deputy Secretary of Defense position, with both deputies performing duties as prescribed by the Secretary of Defense.