Walter Harris was a student of Sydenham and one of those advised by him to study Don Quixote as a preparation for the study of medicine. He was born in 1647 at Gloucester, England; was educated at Westminster School and New College, Oxford, and received his B.A. in 1670. He changed his creed to become a Roman Catholic, resigned his fellowship and went to France to study medicine, where he received his doctor's degree at Bourges in 1675. The next year he returned to London and in 1678, when, as a result of the Oates plot, all Roman Catholics were ordered to leave London, he recanted and published his "Farewell to Popery."
He received a doctor's degree from Cambridge in 1679, and the following year he was a candidate of the College of Physicians. He played an important part in the College, as he was censor in 1688, 1698, 1700,