U.S. banker and diplomat, founder in 1837 of the banking house of August Belmont & Company, in New York City.

At 14 he entered the banking house of the Rothschilds at Frankfurt am Main and later transferred to the Naples office. In 1837 he moved to New York and opened a small office on Wall Street, where he served as American agent for the Rothschilds and laid the foundations for his own banking house. He took an active interest in politics as a Democrat. From 1853 to 1855 he was chargé d'affaires for the United States at The Hague and from 1855 to 1858 he served as resident minister there. He was opposed to slavery and supported Stephen A. Douglas (Douglas, Stephen A), but after the U.S. Civil War began he became a loyal supporter of President Lincoln (Lincoln, Abraham), exerting strong influence upon merchants and financiers in England and France in favour of the Union.

His eldest son, Perry Belmont (1851–1947), was a member of Congress (1881–88) and became U.S. minister to Spain in 1888–89. Another son, August Belmont (1853–1924), took a prominent part in financing and building the New York subway.