The 1856 Democratic National Convention was a presidential nominating convention that met from June 2 to June 6 in Cincinnati, Ohio. It was held to nominate the Democratic Party's candidates for president and vice president in the 1856 election. The convention selected former Secretary of State James Buchanan of Pennsylvania for president and former Representative John C. Breckinridge of Kentucky for vice president.

The 1856 United States presidential election was the 18th quadrennial presidential election, held on Tuesday, November 4, 1856. In a three-way election, Democrat James Buchanan defeated Republican nominee John C. Frémont and Know Nothing nominee Millard Fillmore. The main issue was the expansion of slavery as facilitated by the Kansas–Nebraska Act of 1854. Buchanan defeated President Franklin Pierce at the 1856 Democratic National Convention for the nomination. Pierce had become widely unpopular in the North because of his support for the pro-slavery faction in the ongoing civil war in territorial Kansas, and Buchanan, a former Secretary of State, had avoided the divisive debates over the Kansas–Nebraska Act by being in Europe as the Ambassador to the United Kingdom.