| Honorific Prefix: | The Right Honourable |
| The Lord Mitchison | |
| Birth Date: | 1894 3, df=yes |
| Birth Name: | Gilbert Richard Mitchison |
| Birth Place: | Staines, Middlesex, England |
| Death Place: | Westminster, London, England |
| Office: | Member of Parliament for Kettering |
| Term Start: | 5 July 1945 |
| Term End: | 15 October 1964 |
| Predecessor: | John Profumo |
| Successor: | Geoffrey de Freitas |
| Parliament: | United Kingdom |
| Party: | Labour |
| Children: | Geoffrey, Denis, Murdoch, Avrion, Lois, and Valentine |
| Nationality: | British |
| Alma Mater: | Eton College New College, Oxford |
| Nickname: | Dick |
Gilbert Richard Mitchison, Baron Mitchison, (23 March 1894 – 14 February 1970) was a British Labour politician.
Born in Staines, Mitchison was educated at Eton College and New College, Oxford, and became a barrister (called to the bar in 1917) and King's Counsel. He served with the Queen's Bays in the First World War, attaining the rank of Major and gaining the Croix de Guerre. He worked in the Ministry of Labour during the Second World War, on the Beveridge manpower survey, and led the Nuffield College social reconstruction survey.
Mitchison stood for Parliament without success in King's Norton at the 1931 and 1935 elections. He was the Labour Member of Parliament for Kettering between 1945 and 1964, beating the young incumbent, John Profumo, at the 1945 election. In Parliament, Mitchison sponsored the New Streets Act as a private member's bill. He was given a life peerage, created Baron Mitchison, of Carradale in the County of Argyllshire on 5 October 1964. He served on the executive of the Fabian Society.
He married the writer Naomi Haldane (daughter of John Scott Haldane and sister of J.B.S. Haldane) in Oxford 1916. They had six children, including four sons: Geoffrey (1918–1927), Denis (1919–2018, a professor of bacteriology), Murdoch (1922–2011) and Avrion (1928–2022), both professors of zoology. Their daughters were Lois and Valentine, the latter of whom married the historian Mark Arnold-Forster. Mitchison died in Westminster aged 75.