Biologist. Born into a remarkable family in Oxford (England), Mitchison was the son of politician Dick Mitchison and the Scottish author Naomi Mitchison (1897 - 1901). His uncle was the geneticist J.B.S. Haldane (1892 - 1964), his elder brother is the bacteriologist Denis Mitchison, and his younger brother is the zoologist Avrion Mitchison. He was educated at Winchester College and Trinity College, Cambridge. He was appointed a lecturer at the University of Edinburgh in 1953 and promoted to the Chair of Zoology ten years later, a position he held until his retirement in 1988.
A pioneer in the field of cellular biology, he studied the mechanisms of growth of yeast and produced numerous scientific papers during his career, together with the classic volume The Biology of the Cell Cycle (1971). He was elected a fellow of the Royal Society of Edinburgh in 1966 and the Royal Society of London in 1978. He also served as a member of the Royal Commission on Environmental Pollution (1974-88). He served as Dean of the Faculty of Science and Engineering at Edinburgh (1984-85).
Since 1975, Mitchison lived in a house of his own design at Ormiston (East Lothian), where he cultivated a fine garden. He died in Edinburgh, with his funeral held at Mortonhall Crematorium. His children include the author Amanda Mitchison.