Peter Dennis Mitchell, FRS (29 September 1920–10 April 1992) was a British biochemist who was awarded the 1978 Nobel Prize for Chemistry for his discovery of the chemiosmotic mechanism of ATP synthesis.

He accepted a research post in the Department of Biochemistry, Cambridge, in 1942, and received the degree of Ph.D. in early 1951 for work on the mode of action of penicillin. In 1955 he was invited by Professor Michael Swann to set up a biochemical research unit, called the Chemical Biology Unit, in the Department of Zoology, Edinburgh University, where he was appointed to a Senior Lectureship in 1961, to a Readership in 1962, although ill health led to his resignation in 1963.
From then to 1965, he supervised the restoration of a Regency-fronted Mansion, known as Glynn House, near Bodmin, Cornwall - adapting a major part of it for use as a research laboratory.