On 3 September 1814, Francis_Scott_Key and John S. Skinner of Baltimore, Maryland, an American prisoner-exchange agent, set sail from Baltimore aboard the sloop HMS Minden flying a flag of truce on a mission approved by U.S. President James Madison. Their goal was to secure the release of Dr. William Beanes, the elderly and popular town physician of Upper Marlboro, a friend of Key's who had been captured in Washington, D.C., and had been accused of harboring British deserters. Key and Skinner boarded the British flagship, HMS Tonnant, on 7 September and spoke with General Robert Ross and Admiral Alexander Cochrane over dinner, while they discussed war plans. At first, Ross and Cochrane refused to release Beanes, but relented after Key and Skinner showed them letters written by wounded British prisoners praising Beanes and other Americans for their kind treatment.

Because Key and Skinner had heard details of the plans for the attack on Baltimore, they were held captive until after the battle, first aboard HMS Surprise, and later back on Minden, after which some British gunboats attempted to slip past the fort and effect a landing in a cove to the west of it, but they were turned away by gunners at nearby Fort Covington, the city's last line of defense. During the rainy night, Key had witnessed the bombardment and observed that the fort's smaller "storm flag" continued to fly, but once the shelling had stopped, he would not know how the battle had turned out until dawn. By then, the storm flag had been lowered, and a larger flag had been raised.

Key was inspired by the American victory and the sight of the large American flag flying triumphantly above the fort. This flag, with fifteen stars and fifteen stripes, is today on display in the National Museum of American History, a treasure of the Smithsonian Institution. It was restored in 1914 by Amelia Fowler, and again in 1998 as part of an ongoing conservation program.

Aboard the ship the next day, Key wrote a poem on the back of a letter he had kept in his pocket. At twilight on 16 September, he and Skinner were released in Baltimore. He finished the poem at the Indian Queen Hotel, where he was staying, and he entitled it "Defence of Fort McHenry."

Key gave the poem to his brother-in-law, Judge Joseph H. Nicholson, who recognized that the words fit the tune of the popular melody "To Anacreon in Heaven," which dated from the mid-1760s, when it had been composed, in London, by John Stafford Smith. Nicholson took the poem to a printer in Baltimore, who anonymously printed broadside copies of it—the song's first known printing—on 17 September; of these, two known copies survive.

On 20 September, both the Baltimore Patriot and The American printed the song, with the note "Tune: Anacreon in Heaven." The song quickly became popular, with seventeen newspapers from Georgia to New Hampshire printing it. Soon after, Thomas Carr of the Carr Music Store in Baltimore published the words and music together under the title "The Star-Spangled Banner." The song quickly became popular, and its first public performance took place in October, when Baltimore actor Ferdinand Durang sang it at Captain McCauley's tavern.

The song gained popularity throughout the nineteenth century and bands played it during public events, such as July 4 celebrations. On 27 July 1889, Secretary of the Navy Benjamin F. Tracy signed General Order #374, making "The Star-Spangled Banner" the official tune to be played at the raising of the flag.

In 1916, Woodrow Wilson ordered that "The Star-Spangled Banner" be played at military and other appropriate occasions. Although the playing of the song two years later during the seventh-inning stretch of the 1918 World Series is often noted as the first instance that the Anthem was played at a baseball game, evidence shows that the "Star Spangled-Banner" was performed as early as 1897 at Opening Day ceremonies in Philadelphia and then more regularly at the Polo Grounds in New York beginning in 1898. Today, the anthem is performed before the first pitch at every game.