Professor Timothy John "Tim" Mitchison, PhD, FRS is a British systems biologist. He is Hasib Sabbagh Professor of Systems Biology at Harvard Medical School in the United States.
Mitchison comes from a family of distinguished biologists; he is the son of Avrion Mitchison, his uncles are Denis Mitchison and Murdoch Mitchison, his great uncle was J.B.S. Haldane and his great-grandfather John Scott Haldane. His grandparents were the politician Dick Mitchison and his wife, the writer Naomi (née Haldane). His younger sister Hannah is also a biologist.
Mitchison was educated at The Haberdashers' Aske's Boys' School and completed his undergraduate degree at Merton College, Oxford. Afterward he moved to the University of California, San Francisco in the United States in 1979, where he worked for the Ph.D. under the supervision of Marc Kirschner. At this time he discovered the Dynamic Instability of Microtubules. Later he worked at the National Institute for Medical Research in London. In the late 1980s he returned to San Francisco to become an assistant professor at UCSF. In the late 1990s he moved to Harvard to become co-director of the Institute for Chemistry and Cell Biology at Harvard Medical School. In 2006 he became deputy chair of the newly formed Department of Systems Biology. He was elected Fellow of the Royal Society in 1997.