Don Alejandro O'Reilly, Governor and Captain-General of the province of Louisiana, appointed, on December 1, 1769, six perpetual regidors or aldermen to form a city council, or cabildo, "for the administration of justice and preservation of order" in the city of New Orleans. These aldermen also were assigned individual administrative and/or judicial responsibilities. The Cabildo annually elected other officers, including judges, an attorney general, and a treasurer. The Cabildo met weekly, "for the purpose of deliberating on all that may concern the public welfare." All decisions made by the Cabildo were to be recorded by the body's secretary in a book of resolutions. The various "decrees, royal provisions, and dispatches, which may be addressed to the corporation either by the governor or other authorized minister," were to be recorded and the originals preserved in the archives of the Cabildo.

The detailed rules, regulations, and instructions for government by the Cabildo, presented to the body by O'Reilly on February 23, 1770, are available in translation in B.F. French's "Historical Collections of Louisiana" Volume 5, pages 254-288 available in the City Archvies & Special Collections under call number LOUR976.3 F87h 1976 v5.

The Cabildo remained in place until 1803, when New Orleans was briefly turned over to France before the Louisiana Purchase.