Robert Porter Patterson was born on February 12, 1891, in Glen Falls, New York. He earned his bachelor's degree from Union College and received a law degree from Harvard University in 1915. He fought in World War I and was awarded the Distinguished Service Cross for heroism. He set up a law practice in New York following the end of the war. During the 1930s, he held judicial posts on various levels. In 1940, President Franklin D. Roosevelt appointed him assistant secretary of war under Henry L. Stimson. After a few months, Patterson assumed the position of Undersecretary of War and was responsible for helping to mobilize military supplies for World War II. He worked closely with Undersecretary of the Navy James Forrestal.

In 1945, President Harry S. Truman appointed Patterson secretary of war. Patterson went on to advocate a strong military presence overseas. When the National Security Act of 1947 unified the armed forces, he refused the new post of secretary of defense due to financial reasons. Patterson returned to the practice of law but remained active in politics as a public advocate of the Truman administration's foreign policy. He died in a plane crash on January 22, 1952.