 The younger son of Congressman Charles S. Dewey and his wife, Marie Suzette de Marigny Hall Dewey, and also a distant relative of New York Governor Thomas E. Dewey, Dewey was born in Chicago.He was educated in Switzerland at Institut Le Rosey, before attending at St. Paul's School (Concord, New Hampshire).He graduated from Yale University, where he studied French history and was a member of the Berzelius Secret Society along with friends such as William Warren Scranton.