Davis's parents moved to Mississippi when he was a boy. He was given a classical education at Transylvania Univ. and was appointed to West Point, where he was graduated in 1828. He spent the next seven years in various army posts in the Old Northwest and took part (1832) in the Black Hawk War. In 1835 he married the daughter of Zachary Taylor, but she died three months later. Davis spent the next 10 years in the comparative quiet of a Mississippi planter's life. In 1845 he married Varina Howell.

Elected (1845) to the House of Representatives, he resigned in June, 1846, to command a Mississippi regiment in the Mexican War. Under Zachary Taylor he distinguished himself both at the siege of Monterrey and at Buena Vista. Davis was appointed (1847) U.S. Senator from Mississippi to fill an unexpired term but resigned in 1851 to run for governor of Mississippi against his senatorial colleague, Henry S. Foote, who was a Union Whig. Davis was a strong champion of Southern rights and argued for the expansion of slave territory and economic development of the South to counterbalance the power of the North. He lost the election by less than a thousand votes and retired to his plantation until appointed (1853) Secretary of War by Franklin Pierce. Throughout the administration he used his power to oppose the views of his Northern Democratic colleague, Secretary of State William L. Marcy. Davis favored the acquisition of Cuba and opposed concessions to Spain in the Black Warrior and Ostend Manifesto difficulties, and he also promoted a southern route for a transcontinental railroad, therefore favoring the Gadsden Purchase. Reentering the Senate in 1857, Davis became the leader of the Southern bloc.

Davis took little part in the secession movement until Mississippi seceded (Jan., 1861), whereupon he withdrew from the Senate. He was immediately appointed major general of the Mississippi militia, and shortly afterward he was chosen president of the Confederate provisional government established by the convention at Montgomery, Ala., and inaugurated in Feb., 1861. Elected regular President of the Confederate States (see Confederacy), he was inaugurated at Richmond, Va., in Feb., 1862. Davis realized that the Confederate war effort needed a strong, centralized rule. This conflicted with the states' rights policy for which the Southern states had seceded, and, as he assumed more and more power, many of the Southern leaders combined into an anti-Davis party.

Originally hopeful of a military rather than a civil command in the Confederacy, he closely managed the army and was involved in many disagreements with the Confederate generals; arguments over his policies raged long after the Confederacy was dead. Lee surrendered without Davis's approval. After the last Confederate cabinet meeting was held (Apr., 1865) at Charlotte, N.C., Davis was captured at Irwinville, Ga. He was confined in Fortress Monroe in Virginia for two years and was released (May, 1867) on bail. The federal government proceeded no further in its prosecution of Davis. After his release he wrote an apologia, The Rise and Fall of the Confederate Government (1881). He was buried at New Orleans, but his body was moved (1893) to Richmond, Va.