Bethe was born in 1906 in Strasbourg, now in France but then part of Germany. He studied physics at the University of Frankfurt and then carried out research at the University of Munich. He spent time at several other universities but because his mother was Jewish he came into conflict with Nazi race laws. He left Germany in 1933 for England and then took up a position at Cornell University near New York in 1935, where he was to remain for the rest of his career.

Between 1935 and 1938 Bethe carried out research on nuclear theory, in which he predicted the probability of different reactions occurring. This led him to his Nobel-prize winning work, the discovery that stars get their energy from a series of six nuclear reactions, the so-called "carbon cycle".

In 1943 he went to work on the Manhattan project, and as head of the theoretical physics division made a crucial contribution towards the development of the bomb. After the war he brought a number of outstanding young scientists from Los Alamos back to Cornell, including Richard Feynman, with whom he developed quantum electrodynamics. During his career, Bethe carried out research across the whole spectrum of physics, from solid state theory and disorder in alloys to solar neutrinos and supernovae.

Bethe was also a strong advocate of arms control. In particular he argued against the development of the hydrogen bomb and clashed with the inventor of that device, Edward Teller. He also helped to persuade the US government to ban atmospheric nuclear tests in 1963 and antiballistic missile systems in 1972, and later opposed President Reagan's "Star Wars" missile defence system.