Michael Henry Knox Irwin (5 June 1931 - ) is a retired GP and former medical director of the United Nations. He is a humanist and secularist activist and a campaigner for voluntary euthanasia.
Irwin's father was William Knox Irwin FRCS, a surgeon and author of medical text books.
Michael Irwin married Elizabeth Naumann in 1958; the marriage was dissolved in 1982. He married Frederica Harlow in 1983. His current partner is Angela Farmer.