Roger John Keynes FMedSci (born 25 February 1951) is a British medical scientist. He is a Fellow of Trinity College, Cambridge, and a professor within the Department of Physiology, Development and Neuroscience.

Kenyes is the third son of four of Richard Keynes and his wife The Hon. Ann Pinsent Adrian, daughter of Edgar Adrian, 1st Baron Adrian and his wife Hester (née Pinsent). Through his father he is a great-great-grandson of Charles Darwin. His elder brother Randal Keynes is a conservationist and author, while his younger brother Simon Keynes is a historian and also a fellow of Trinity, as indeed was their father Richard.