[1] Szilard initially attended Palatine Joseph Technical University in Budapest, but his engineering studies were interrupted by service in the Austro-Hungarian Army during World War I.

Szilard coined and submitted the earliest known patent applications and the first publications for the concept of the electron microscope (1928), the cyclotron (1929), and also contributed to the development of the linear accelerator (1928) in Germany.

Foreseeing another war in Europe, Szilard moved to the United States in 1938, where he worked with Enrico Fermi and Walter Zinn on means of creating a nuclear chain reaction.

According to Theodore Puck and Philip I. Marcus, Szilard gave essential advice which made the earliest cloning of the human cell a reality.

Szilard founded Council for a Livable World in 1962 to deliver "the sweet voice of reason" about nuclear weapons to Congress, the White House, and the American public.

His middle-class Jewish parents, Lajos (Louis) Spitz, a civil engineer, and Tekla Vidor, raised Leó on the Városligeti Fasor in Pest.

[6][7] With World War I raging in Europe, Szilard received notice on January 22, 1916, that he had been drafted into the 5th Fortress Regiment, but he was able to continue his studies.

[11] In January 1919, Szilard resumed his engineering studies, but Hungary was in a chaotic political situation with the rise of the Hungarian Soviet Republic under Béla Kun.

He was convinced that socialism was the answer to Hungary's post-war problems, but not that of Kun's Hungarian Socialist Party, which had close ties to the Soviet Union.

[12] When Kun's government tottered, the brothers officially changed their religion from "Israelite" to "Calvinist", but when they attempted to re-enroll in what was now the Budapest University of Technology, they were prevented from doing so by nationalist students because they were Jews.

[13] Convinced that there was no future for him in Hungary, Szilard left for Berlin via Austria on December 25, 1919, and enrolled at the Technische Hochschule (Institute of Technology) in Berlin-Charlottenburg.

In 1928 he submitted a patent application for the linear accelerator, not knowing of Gustav Ising's prior 1924 journal article and Rolf Widerøe's operational device,[23][24] and in 1929 applied for one for the cyclotron.

As a result, Szilard never received the Nobel Prize, but Ernest Lawrence was awarded it for the cyclotron in 1939, and Ernst Ruska for the electron microscope in 1986.

[34] He wanted to carry out a systematic survey of all 92 then-known elements in order to find one that can allow the chain reaction, at an estimated cost of $8000, but he did not for lack of funds.

[50] In early 1938, Szilard would settle down at "what would become a haven for much of the rest of his life" when he took a room at the King's Crown Hotel in New York City, being near Columbia University where he now conducted research without a formal title or position.

[50] That same month, Niels Bohr brought news with him to New York that nuclear fission had accidentally been observed by chemists Otto Hahn and Fritz Strassmann at the Kaiser Wilhelm Institute for Chemistry in Berlin on December 19, 1938.

[51] When Szilard found out about it on a visit to Wigner at Princeton University, he immediately realized that uranium might be the element capable of sustaining a chain reaction.

[53] Szilard and Zinn conducted a simple experiment on the seventh floor of Pupin Hall at Columbia, using a radium–beryllium source to bombard uranium with neutrons.

As a back-up plan, Szilard also considered where he might find a few tons of heavy water; deuterium would not absorb neutrons like ordinary hydrogen but would have the similar value as a moderator.

With the help of Wigner and Edward Teller, he approached his old friend and collaborator Einstein in August 1939, and persuaded him to sign the letter, lending his fame to the proposal.

[60] A 1940 Army intelligence report on Fermi and Szilard, prepared when the United States had not yet entered World War II, expressed reservations about both.

[64] Like the German researchers, Fermi and Szilard still believed that enormous quantities of uranium would be required for an atomic bomb, and therefore concentrated on producing a controlled chain reaction.

[68] When the coolant issue became too heated, Compton and the director of the Manhattan Project, Brigadier General Leslie R. Groves, Jr., moved to dismiss Szilard, who was still a German citizen, but the Secretary of War, Henry L. Stimson, refused to do so.

Single people living together was frowned upon in the conservative United States at the time and, after they were discovered by one of her students, Szilard began to worry that she might lose her job.

[93] His comments, as well as those of Hans Bethe, Harrison Brown, and Frederick Seitz (the three other scientists who participated in the program), were attacked by the Atomic Energy Commission's former Chairman David Lilienthal, and the criticisms plus a response from Szilard were published.

[95] Physicist W. H. Clark suggested that a 50 megaton cobalt bomb did have the potential to produce sufficient long-lasting radiation to be a doomsday weapon, in theory,[96] but was of the view that, even then, "enough people might find refuge to wait out the radioactivity and emerge to begin again.

[97][98] Szilard published a book of short stories, The Voice of the Dolphins (1961), in which he dealt with the moral and ethical issues raised by the Cold War and his own role in the development of atomic weapons.

[105] Szilard spent his last years as a fellow of the Salk Institute for Biological Studies in the La Jolla community of San Diego, California, which he had helped create.

[106] Szilard founded Council for a Livable World in 1962 to deliver "the sweet voice of reason" about nuclear weapons to Congress, the White House, and the American public.

[108] In February 2014, the library announced that it received funding from the National Historical Publications and Records Commission to digitize its collection of his papers, ranging from 1938 to 1998.