Onora Sylvia O'Neill, Baroness O'Neill of Bengarve (born 23 August, 1941) is a cross-bench member of the House of Lords. She was made a Life Peer in 1999.

She studied philosophy, psychology and physiology at Oxford, and went on to complete a doctorate at Harvard, with John Rawls as supervisor. She is a former professor of philosophy and is the Principal of Newnham College, Cambridge. She has written widely on political philosophy and ethics, international justice, bioethics and the philosophy of Immanuel Kant. Her books include:

• Bounds of Justice (2000)
• Towards Justice and Virtue (1996)
• Constructions of Reason: Exploration of Kant's Practical Philosophy (1989)
• Faces of Hunger: An Essay on Poverty, Development and Justice (1986)