Louisianians consider the Sala Capitular one of their most prestigious settings for official ceremonies, evidenced by the fact that the final transfers of the colony were held in it: from Spain to France on November 30, 1803, and from France to the United States on December 20, just twenty days later. The Sala Capitular also functioned as a courtroom, first for the cabildo under Spanish rule (1799–1803), then the superior court in the territorial period (1803–1812), and later the Louisiana Supreme Court after the Civil War (1868–1910).
 

The Louisiana Purchase

Emperor Napoleon Bonaparte had a vision of a renewed western empire for France, and his schemes included the recapture of Louisiana from Spain. Control over this vast territory would halt the westward expansion of the young United States and would supply French colonies in the West Indies with the goods they needed. In 1800, Napoleon signed the secret Treaty of Ildefonso with Spain, an agreement that stipulated that France would provide Spain with a kingdom for the son-in-law of Spain's king if Spain would return Louisiana to France. However, Napoleon's plan collapsed when the twelve-year revolt of slaves and free blacks in the French colony of Saint-Domingue succeeded, forcing French troops to return defeated to France and preventing them from reaching their ultimate destination—Louisiana—and from being able to defend it. As Napoleon's New World empire disintegrated, the loss of Haiti made Louisiana unnecessary.

The United States wanted to acquire the area near New Orleans primarily to guarantee its right to sail vessels down the Mississippi River through Spanish territory and unload goods at New Orleans for shipment to the Atlantic coast and Europe. Moreover, the United States wanted to possess the entire territory of Louisiana because so many American settlers and merchants were already in the region and because of its vital geographic position at the mouth of the Mississippi River.

The United States discovered the transfer of Louisiana from Spain to France and sent Robert Livingston to France in 1801 to try to purchase New Orleans. Napoleon initially refused, leading President Thomas Jefferson to send James Monroe to secure the deal. However, in April 1803, just days before Monroe was to arrive in Paris, Napoleon offered to sell the United States not only New Orleans but all of Louisiana. Napoleon's minister of the treasury, the Marquis de Barbé-Marbois, dealt with Livingston and Monroe over terms of the Louisiana Purchase. The United States purchased Louisiana for $11,250,000 and assumed claims of its own citizens against France up to $3,750,000, for a total purchase price of $15 million.

On November 30, 1803, Spain's representatives, Governor Manuel de Salcedo and the Marqués de Casa Calvo, officially transferred Louisiana to France's representative, Prefect Pierre Clément de Laussat, in the Sala Capitular in the Cabildo. Although Laussat had been instructed to transfer Louisiana to the United States the next day, twenty days actually separated the transfers, during which time Laussat became governor of Louisiana and created a new town council.

Thomas Jefferson selected William Charles Cole Claiborne, former governor of the Mississippi territory and highest-ranking civilian official in the vicinity, to govern lower Louisiana. Backing Claiborne with military power was General James Wilkinson. On December 20, 1803, again in the Sala Capitular, these two commissioners signed the transfer document with Laussat, giving lower Louisiana officially to the United States. The United States took formal possession of the full territory of Louisiana, although its boundaries were vaguely defined, in St. Louis three months later, when France handed over the rights to upper Louisiana.

Between April 10 and 15, 1825, the Marquis de Lafayette, a Frenchman who assisted the Americans with their war for independence and became a hero of the French Revolution, resided in the Cabildo during a visit to New Orleans. Lafayette stayed in the city as a part of his tour of the United States in 1824 and 1825.

Laborers converted the Sala Capitular into a lavish drawing room where Lafayette met various delegations during his stay, including a deputation of free men of color, "who, in 1815, courageously assisted in the defense of the city." The room was completely redecorated to fit its elegant purpose of hosting Lafayette and his visitors. New wall hangings and furniture were procured, and wallpaper, draperies, carpets, and chandeliers were installed for the five-day stay.

The Louisiana State Supreme Court met in the Sala Capitular from 1868 to 1910. During the course of its tenure here, the Supreme Court heard several important cases that in turn went on to the United States Supreme Court to become landmark cases in American history. Among these was Plessy v. Ferguson, which was first argued in 1892. The case tested legislation passed in Louisiana in 1890 that permitted separate railroad cars for whites and blacks.

In March 1892, Homer Adolph Plessy, a light-skinned New Orleans black man who was actively involved in the civil rights movement, purchased a ticket on the East Louisiana Railroad, sat in a whites-only coach, and refused to move. In the criminal suit that resulted, Judge John H. Ferguson upheld Louisiana's segregation law, and Plessy appealed the ruling to the Louisiana State Supreme Court, housed in the Cabildo, which also ruled against Plessy, stating that his rights had not been violated. When the United States Supreme Court decided the case in 1896, they upheld the state's ruling in favor of Ferguson, thereby sanctioning the doctrine of "separate but equal" and legalizing segregation in the United States for more than the next fifty years.

Between 1834 and 1890, what collectively is called the Myra Clark Gaines Case went to the Louisiana Supreme Court five times and to the United States Supreme Court seventeen times, making the case the longest-running lawsuit in the history of the United States Supreme Court. One of the five lawsuits heard by the Louisiana Supreme Court was heard in the Sala Capitular. The cases arose over Myra Clark Gaines' claims to her father's estate, and although Clark won in the end, she expended the fortune that her second husband, General Edmund Pendleton Gaines, left her and died penniless in 1885, five years before the final lawsuit was decided in her favor.
 

Napoleon

In imitation of French king Louis XIV, Napoleon worked hard to develop his own legend and fashion his persona. He used the press, the arts, and the church to boost his fame. Like most legends, the Napoleonic one is part fact, part fiction. 

According to popular legend, some of Napoleon's former officers who were residing in New Orleans schemed to rescue him from exile on the island of St. Helena and bring him to Louisiana. Three days before a ship manned by Louisiana pirates and waiting off the coast of St. Helena could sail, Napoleon died. The ship was to carry Napoleon to New Orleans, where he would have lived in a house in the French Quarter given to him by the city's mayor. This famous building is now a bar and restaurant known as the Napoleon House.

One of the most legendary artifacts on display in the Cabildo is the death mask of the French Emperor Napoleon Bonaparte. City authorities moved the death mask, along with their offices, from the Cabildo in 1853. During the tumult that accompanied the Civil War, the mask disappeared. A former city treasurer spotted the mask in 1866 as it was being hauled to the dump in a junk wagon. Rather than return the mask to the city, the treasurer took the mask home and put it on display there. Eventually, Napoleon's death mask wound up in the Atlanta home of Captain William Greene Raoul, president of the Mexican National Railroad.

Finally, in 1909, Napoleon's death mask made its way back to the Crescent City. Captain Raoul read a newspaper article about the missing mask and wrote to the mayor of its whereabouts. In exchange for suitable acknowledgment, Raoul agreed to donate the death mask to New Orleans. The mayor transferred the mask to the Louisiana State Museum that year.