Jacob Klein was born in Liepāja, Latvia. He studied at the universities of Berlin and Marburg, where he received his doctorate in 1922. He was Martin Heidegger's star graduate student in philosophy and became one of the world's pre-eminent interpreters of Plato. He also became a lifelong friend of the political philosopher Leo Strauss. He had to flee Nazi persecution, as did many other Jewish scholars, and emigrated to the USA, where he became a member of the faculty at St. John's College in Annapolis, Maryland. He served as dean from 1949 to 1958.