below is a present day aerial of the location of the Royal St Neighborhood.

Dear Brigitte,
Casa Calvo was a street in Faubourg Marigny that was named for a man who was sent to New Orleans for a temporary job. In 1799, he was needed to act as interim governor of Louisiana until the permanent one arrived. His entire name -- a very fancy one indeed -- was Sebastian de la Puerta Y O'Farril, Marquis de Casa Calvo. He was replaced by Don Juan Manuel de Salcedo, who arrived in June 1801 and had a brief and undistinguished career as Louisiana's last Spanish governor.
Casa Calvo was one of the streets named by Bernard Xavier Philippe de Marigny de Mandeville, a Creole lad, born in 1785, who inherited a great deal of money and property from his very rich papa. However, Bernard was a wild youth who lived extravagantly, gambled away much of his inheritance, and was reduced in 1808 to subdividing his land and selling the lots. He created his separate faubourg with unique street names that included Bagatelle, Love, History, Peace, Good Children, Victory, Great Men and Craps. On Nov. 20, 1852, Rue Casa Calvo was renamed Royal as an extension of the street in the French Quarter. Likewise, the other streets in Faubourg Marigny were also renamed.
The street you are not sure of sounds a lot like Louisa Street, which intersects with Royal Street downriver in the historic district now known as Bywater. The history of the area goes back to just after the founding of the city in 1718, when gifts of land were made to private owners. By the 19th century, there were at least six Creole plantations in the area, which was known collectively as Faubourg Washington. One of the plantation owners was deClouet, and the street was named for Louisa deClouet.
Although the name Casa Calvo was changed in 1852, folks may have still been calling it by its old name when your ancestor died.
From Blake in NOLA: about the name change of Casacalvo to Royal Street
Coroner's Report: State of Louisiana
Parish of New Orleans - City of New Orleans

I, Dr. E. D. Beach Coroner of the Parish of Orleans having notice of the death of Arthur Marmion aged eighty years, a native of Ireland found dead in a house on 669 Casa calvo street and after making due inquiry and diligence concerning the death of said Arthur Marmion do hereby certify that guilt is attached to any person by reason of said death and that an
inquest is uneccessary,  he having died a natural death by Debility and Old age"
New Orleans October 30th, 1862

(this was during the time Butler the Beast held the city of NOLA. Because 3 people died in the same area as Arthur on the same day, there was concern over foul play and a Coroners Inquest was called for, but there was no foul play found)
at right pictured is a Royal Street Neighborhood. We believe Arthur was paying a visit to a Mr D. Farrar a man from Liverpool England, who was a Customs House Officer. Arthur died at 669 Casa Calvo (aka Royal) Street.
Arthur Marmions obit. Oct 29, 1862. died in NOLA while Gen Butler (Butler the beast) held the city