Born in New York City, N.Y., 1793, the Northern-born Slidell rose to prominence as a Louisiana politician in the decades before the Civil War. A lawyer who began his career as a businessman, he moved to New Orleans in 1819 after his mercantile interests failed during the War of 1812.

Slidell lost a bid for Congress in 1828 and was frustrated in his political ambitions until 1843, when he was elected to the U.S. House of Representatives. As a states-rights Democrat he supported James K. Polk for the presidency in 1844 and used questionable legal means to assure him a Louisiana majority in the presidential election. Polk appointed Slidell commissioner to Mexico, with instructions to settle the Texas-Mexico boundary dispute and purchase New Mexico and California. The mission failed when the Mexican government refused to accept his credentials.

Slidell was elected to the Senate in 1853 and cast his lot with other pro-Southern congressmen to repeal the Missouri Compromise, acquire Cuba, and admit Kansas under the Lecompton constitution. In the 1860 campaign Slidell supported Democratic presidential candidate John C. Breckinridge, but remained a pro-Union moderate until Abraham Lincoln's election pushed the Southern states into seceding. Siding with the South, Slidell accepted a diplomatic appointment to represent the Confederacy in France.

His arrival in Europe was delayed by the TRENT AFFAIR, when he and fellow diplomat James M. Mason were removed from their British-registered ship by the commander of a Federal vessel. Once there, he found the French sympathetic to the Confederate cause, but met with little success in securing extensive military aid or the Franco-Confederate treaty of alliance he sought. Slidell remained in France lobbying throughout the war. Though he was never able to accomplish a Franco-Confederate liaison, and though many of his Confederate colleagues distrusted him, Slidell, through his political abilities and bolstered by his marriage to a Louisiana Creole woman, arranged some Confederate financing through private French interests.

Uncertain of his safety at home after the war, Slidell and his family stayed in Paris. He never sought pardon from the Federal government for his Confederate service, dying in London, England, 29 July 1871.