Oliphant, Mark (1901-2000), an Australian nuclear physicist, was a key figure in the development of the atomic bomb. Later, Oliphant ardently opposed the further use of nuclear weapons.

The oldest of five sons of a civil service clerk and a schoolteacher, Marcus (Mark) Laurence Elwin Oliphant attended secondary schools in Unley and Adelaide. Having graduated with honors from Adelaide University, he earned a doctorate from Trinity College, Cambridge, in 1929. At Cambridge he joined the Cavendish Laboratory, which was an international center in nuclear and experimental physics under its director, Ernest Rutherford. Oliphant became assistant director of research there in 1935. His own research involved the design of heavy high-voltage apparatus, which enabled him both to produce intense beams of protons and of deuterium nuclei and to study their interactions with other light nuclei. He discovered a new form of hydrogen (tritium) and helium 3.

Elected a fellow of the Royal Society in 1937, Oliphant moved that year to Birmingham University as Poynting Professor of Physics, a post he held until 1950. As World War II (1939–1945) approached, Oliphant did microwave research that would transform radar into a war-winning device. His endorsement of the Frisch-Peierls memorandum, which argued the feasibility of the uranium bomb, underlay the British program to develop the atomic bomb. He later was a leader of the British delegation to the U.S. War Department's Manhattan Project. Following the detonation of bombs against Japan in 1945, Oliphant became a founding member of the Pugwash Movement of scientists opposed to nuclear weapons and an opponent of scientific research with military applications. He helped to found the Australian Academy of Sciences in 1954 and was its first president (1954–1956).

As director of the Research School of Physical Sciences at Australian National University in Canberra (1950–1963), Oliphant oversaw the building of a particle accelerator. He retired from the university in the late 1960's. Knighted in 1959, he served as governor of South Australia (1971–1976).