U.S. senator from Connecticut (1879–1905) who introduced the Platt Amendment (q.v.), which became the basis for the withdrawal of U.S. troops from Cuba following the Spanish–American War of 1898.

Platt began the practice of law in Meriden, Conn., in 1850 and was active in Connecticut politics, serving as secretary of state (1857), state senator (1861–62), and member of the state House of Representatives (1864, 1869). In 1879 he was elected as a Republican to the U.S. Senate. Although principally remembered in connection with the Platt Amendment, he also sponsored important legislation relating to patents and copyrights, including the international copyright act of 1891, and was chairman of the committee on territories (1887–93), which recommended the admission to the Union of six new Western states. He was also instrumental in the passage of the Sherman Silver Purchase Act of 1890. One of the “Big Four” leaders of the Senate—with Nelson W. Aldrich, William B. Allison, and James C. Spooner—Platt was regarded as a “stand-pat” conservative and was admired for his integrity and independence.