Emilio Segré was born in Tivoli, Italy, on 1st February, 1905. He studied physics at University of Rome where he was taught by Enrico Fermi.
After receiving his doctorate in physics in 1928 Segré served in the Italian Army. In 1929 Segré began teaching at the University of Rome. Over the next few years he worked in the field of atomic spectroscopy. In 1934 he began collaborating with Enrico Fermi on neutron research. This included experiments where elements such as uranium were bombarded with neutrons. By 1935 they had discovered slow neutrons, which have properties important to the operation of nuclear reactors.
In 1936 Segré became director of the physics laboratory at the University of Palermo. The following year he discovered technetium.
Segré disapproved of the fascist rule of Benito Mussolini and in 1938 he emigrated to the United States and became a research associate at the University of California. In 1940 he was a member of the team that discovered the element astatine. Soon afterwards he helped discover plutonium-239.
In 1943 Segré joined the Manhattan Project where he worked with Edward Teller, Enrico Fermi, David Bohm, Robert Oppenheimer, Niels Bohr, James Franck, Leo Szilard and Klaus Fuchs in developing the atom bombs dropped on Hiroshima and Nagasaki.