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.
