Egon Bretscher was born on 23 May 1901 in Zürich, the second son of Julius Bretscher and Anna Bretscher (née Martin).

He was educated at Gymnasium Zürich and Eidgenössische Technische Hochschule (ETH Zürich), where he gained his diploma in chemical engineering in 1925. He then studied at the department of chemistry at the University of Edinburgh, where he was taught by Sir James Walker and received his PhD in 1927. In 1931, he married Hanna Greminger, with whom he had three sons and two daughters. Egon Bretscher started his career as an Assistant and Privatdozent für Physik at the ETH Zürich, where he worked from 1929 to 1936. He became a Fellow at the Rockefeller Foundation and was based at the Cavendish Laboratory in Cambridge, 1934-5. Bretscher returned to Cambridge as a Clerk Maxwell Scholar, 1936-9, and lecturer in Nuclear Physics, 1949-44. Through his work on nuclear physics, he was involved in the British atomic bomb research project 'Tube Alloys' and became a member of the Maud Committee as well as of the British Mission to the Manhattan District Scientific Laboratory at Los Alamos, New Mexico. He worked at Los Alamos in Fermi’s Advanced Development Division, 1944-6. After the war, Bretscher returned to Britain and joined the Atomic Energy Research Establishment, Harwell, as head of the Chemistry Division, 1947-8, and then as head of the Nuclear Physics Division, 1948-66. He retired in 1966.

Egon Bretscher was awarded a CBE in 1966. He died on 16 April 1973.