In 1919 he began studyingelectrical engineering and physics in Budapest before moving to Berlin to study under Albert Einstein, Max Planck and Max von Laue. In 1923 he began carrying out x-ray diffraction experiments at Kaiser-Wilhelm Institute for Chemistry. The following year he became Laue's assistant at the Institute for Theoretical Physics in Berlin.
Szilard was appointed a lecturer in physics in 1929. He also worked with Albert Einstein and they eventually developed a home refrigerator without moving parts. Szilard became friends with H.G. Wells and they discussed the possibility of establishing an international movement of progressive intellectuals.
When Adolf Hitler gained power in 1933 Szilard left Nazi Germany and moved to England. The following year he published his views on the possibility of achieving neutron chain reaction. Although his ideas were rejected by Ernest Rutherford, he began his experiments at St. Bartholomew's Hospital and in 1934 developed a method of artificially producing radioactive isotopes.
In 1938 he emigrated to the United States where he taught nuclear physics at Columbia University. Soon afterwards Szilard heard about the research being carried out by Otto Hahn and Fritz Strassmann at the Kaiser Wilhelm Institute for Chemistry in Germany that appeared to show that the uranium nuclei could be split when bombarded with neutrons. He also read and article by Otto Frisch and Lise Meitner, explaining the theory of uranium fission. In the paper they argued that by splitting the atom it was possible to use a few pounds of uranium to create the explosive and destructive power of many thousands of pounds of dynamite.
Szilard contacted Albert Einstein about these developments. On 2nd August, 1939, Szilard, Einstein, and another Jewish scientist, Eugene Wigner, wrote a joint letter to President Franklin D. Roosevelt, about the developments that had been taking place in nuclear physics. They warned Roosevelt that scientists in Germany were working on the possibility of using uranium to produce nuclear weapons.
In 1942 Szilard and Enrico Fermi began building the first fission reactor in Chicago. The following year Szilard joined the Manhattan Project. Over the next two years he worked with Robert Oppenheimer, Edward Teller, Otto Frisch, Felix Bloch, Enrico Fermi, David Bohm, James Chadwick, James Franck, Emilio Segre, Niels Bohr, Eugene Wigner and Klaus Fuchs in developing the atom bomb.
In 1945 Szilard and James Franck circulated a petition among the Manhattan Project scientists opposing the use of the atomic bomb on moral grounds. However, the advice was ignored by Harry S. Truman and the bombs were dropped on Hiroshima and Nagasaki.
After the war Szilard became a leading campaigner in favour of international control of nuclear weapons. In 1947 he wrote Letter to Stalin, proposing methods for reducing tensions between the United States and the Soviet Union.
Szilard helped organize the first of the Pugwash conferences in 1957. These conferences enabled top scientists from all countries to discuss peace and world security.
In 1962 Szilard founded the Council for Abolishing War. He also published a book on the misuse of scientific knowledge entitled The Voice of Dolphins (1961). Leo Szilard died in La Jolla, California, on 30th May, 1964.