James Brown Clay (November 9, 1817 – January 26, 1864) was a Democratic Party member of the United States House of Representatives from Kentucky.
Born in Washington, D.C., while his father, Henry Clay, was serving in the United States Congress, James Brown Clay was named for the husband of his maternal aunt, James Brown. His brothers were Henry Clay, Jr. and John Morrison Clay. Clay attended a boys' school associated with Kenyon College, Gambier, Ohio (founded by family friend Bishop Philander Chase). Later, Clay attended Transylvania University, Lexington, Kentucky. He worked at a countinghouse in Boston from 1832 to 1834 before studying law and being admitted to the bar. He practiced law with his father in Lexington, Kentucky. In 1843, Clay married Susan Maria Jacob, the daughter of Louisville's first millionaire and sister of its later mayor, Charles Donald Jacob. The couple eventually had ten children.
Clay served as Chargé d'Affaires to Portugal from August 1, 1849, to July 19, 1850. He farmed in Missouri in 1851 and 1852 before returning to Lexington. Clay had been a lifelong member of the Whig Party — the party of his father. But when the Whig Party disintegrated following Henry Clay's death, and due to the controversy surrounding the Kansas-Nebraska Act, James B. Clay joined the Democratic Party. He was elected as a Democrat to the Thirty-fifth Congress (March 4, 1857 – March 4, 1859). Clay did not run for renomination in 1858 and declined an appointment by President James Buchanan to a mission to Germany. Clay served as a member of the Peace Conference of 1861 held in Washington, D.C., an attempt to prevent the impending American Civil War. During the Civil War Clay supported the Confederacy and was commissioned to raise a regiment. His ill-health from tuberculosis prevented him from doing so. Clay died in Montreal, Canada, where he had gone for his health. He is interred at his family plot in Lexington Cemetery.