Australian moral philosopher, professor at Princeton's Center for Human Values since 1999, and the most widely read living utilitarian. Singer's career has been an unusually direct argument for the proposition that careful ethical reasoning ought to change how ordinary people live — and his books have, in fact, changed how a substantial number of them do.
Animal Liberation (1975) is the book for which Singer is most widely known and remains among the most consequential philosophical works of its half-century in terms of practical effect. The argument is straightforwardly utilitarian: the capacity to suffer, not species membership, is what makes a being's interests morally considerable; the systematic discounting of nonhuman animal suffering — speciesism, on the model of racism and sexism — is therefore a moral error of the same logical structure; the contemporary practices of factory farming and most animal experimentation cannot survive moral scrutiny. The book launched the modern animal-rights movement and shaped a generation of subsequent activism, philosophy, and (eventually) regulation and consumer behavior.
Practical Ethics (1979, multiple revised editions) extended utilitarian analysis across abortion, euthanasia, global poverty, and environmental ethics, and is the most widely assigned applied-ethics textbook in the English-speaking world. The arguments are deliberately plain and willing to follow premises into uncomfortable conclusions — a stance that has made Singer the target of sustained protest, particularly from disability-rights advocates who challenge his arguments about severely disabled newborns. The Life You Can Save (2009) and his earlier essay "Famine, Affluence, and Morality" (1972) made the case for substantial personal giving against global poverty as a moral obligation rather than a supererogatory virtue, and helped seed what later became the effective altruism movement.
Singer is the contemporary public face of the utilitarian tradition that runs from Bentham through Mill and Sidgwick. He is unusual among prominent academic philosophers in regarding the discipline as ethically obligated to address the actual moral problems of the moment in language nonphilosophers can follow.