Jefferson Allen McMahan (born 30 August 1954) is an American philosopher. He is currently White's Professor of Moral Philosophy at the University of Oxford.

McMahan has published extensively on topics of interest to effective altruism, such as population ethics;^[1][2] existential risk from nuclear war;^[3][4] animal ethics^[5]—including the ethics of eating animals,^[6] the moral status of animals,^[7] and wild animal welfare^{[8][9][10][11]}—; and the demandingness of morality.^[12] He has also published a response to various criticisms of effective altruism.^[13]