Reginald Robin Farquharson (3 October 1930 – 1 April 1973) was an academic whose interest in mathematics and politics led him to work on game theory and social choice theory. He wrote an influential analysis of voting systems in his doctoral thesis, later published as Theory of Voting, and conjectured the Gibbard–Satterthwaite theorem together with the philosopher and logician Michael Dummett.

Farquharson diagnosed himself as suffering from bipolar disorder (manic depression), and episodes of mania made it difficult for him to obtain a permanent university position and also resulted in him losing commercial employment. In later years, he dropped out of mainstream society, and became a prominent counter-cultural figure in late-1960s London. Farquharson wrote an account of his unconventional life in his 1968 book, Drop Out!, in which he described a week of being homeless in London. In 1973 he died from burns associated with an arson, for which two persons were convicted of unlawful killing.

Robin Farquharson was educated at Michaelhouse, Natal, South Africa, 1944–46. He earned a B.A. in South Africa from Rhodes University College, Grahamstown (1947–50). Subsequently studying at Brasenose and Nuffield Colleges, University of Oxford (1950–53), he obtained a second-class B.A. honours PPE degree. For his B.A. 1953–54 (?), his studies at this time were overseen by David Butler of Nuffield College, Oxford University. His D.Phil. was awarded in June 1958 from Nuffield College for his thesis entitled "An Approach to a Pure Theory of Voting Procedures". He was given a Research Fellowship at Churchill College, Cambridge in 1964. He also studied at the Sorbonne in Paris.

While an undergraduate at Oxford, Farquharson was a contemporary of John Searle, Rupert Murdoch, and Sir Michael Dummett. In the preface to Probability and Scientific Inference (1957) George Spencer Brown thanked Farquharson for his help in discussing and clarifying some of the ideas in the book, before publishing his paper.

Farquharson wrote a monograph on the analysis of voting procedures and several papers, including a notable paper with Michael Dummett that conjectured the Gibbard–Satterthwaite theorem.

Farquharson published influential articles on the theory of voting: in particular, in an article with Michael Dummett, he conjectured that deterministic voting rules with more than three issues faced endemic strategic voting. The Dummett–Farquharson conjecture was proved by Allan Gibbard, a philosopher and former student of Kenneth J. Arrow and John Rawls, and by Mark Satterthwaite, an economist.

After the establishment of the Farquarson-Dummett conjecture by Gibbard and Sattherthwaite, Michael Dummett contributed three proofs of the Gibbard–Satterthwaite theorem in his monograph on voting.

In the field of political game theory, Farquharson's main contribution was his exposition of the Condorcet paradox regarding the sincerity of voters. The problem was initially raised by Pliny the Younger and then picked up again in the political pamphlets of Reverend Charles Lutwidge Dodgson (Lewis Carroll), who was a significant influence on Farquharson.