U.S. electrical engineer and first president of the Bell telephone Laboratories, Inc., who directed research in telephony, telegraphy, and radio and television communications.

After receiving the B.A. in 1898 from Throop Polytechnical Institute (now the California Institute of Technology) and the Ph.D. in 1902 from the University of Chicago, Jewett taught at the Massachusetts Institute of Technology, Cambridge. In 1904 he began work with the American Telephone and Telegraph Company, where he designed long-distance telephone lines, including a transcontinental line from New York to San Francisco. He also worked on telephone repeaters and directed the research that led in 1915 to the first transatlantic telephone call.

During World War I Jewett was commissioned in the U.S. Signal Corps and worked on telephone systems and the first tests for aircraft radiophones. After the war, as president of the Bell Telephone Laboratories (1925–40) and vice president of American Telephone and Telegraph, he directed early work on the dial telephone, sound motion pictures, the transmission of pictures over telephone wires, the electric phonograph, and submarine telephone cables. This work helped establish the Bell laboratories as a major industrial research centre.

From 1933 until 1935 Jewett served on President Franklin Roosevelt's Science Advisory Board and served as president of the National Academy of Sciences from 1939 to 1947. After the Second World War he advocated civilian rather than military control of scientific research.