Renwick was not formally trained as an architect, but his ability and interest in building design were nurtured through his cultivated upbringing, which granted him early exposure to travel, and through a broad cultural education that included architectural history.

Renwick went on to design St. Patrick's Cathedral, on the corner of Fifth Avenue and 51st Street, which is considered his most notable architectural achievement.

Renwick also designed the St. Anthony Hall, the first chapter house for Delta Psi, the secret fraternal college society founded at Columbia University in 1847.

Even though the 1879 structure at 29 East 28th Street is marred now by a street level storefront, Christopher Gray wrote in The New York Times in 1990 that, "Old photographs show a high stoop arrangement with the figure of an owl on the peaked roof and a plaque with the Greek letters Delta Psi over the windowless chapter room.

In 1879, The New York Tribune called it French Renaissance, but the stumpy pilasters and blocky detailing suggest the Neo-Grec style then near the end of its popularity."

In 1899, the fraternity moved to a new chapter house on Riverside Drive and for a few years the original building was kept as a clubhouse for graduate members.

Renwick was also the designer of the bell tower of the Cathedral Basilica of St. Augustine in Florida, which was commissioned by Standard Oil partner Henry M. Flagler who was building luxury hotels in the historic city at the time.

Renwick and his wife Anna Aspinwall lived and owned property in the lighthouse area on Anastasia Island in Florida.

In Spring 1890, Renwick listened to Franklin W. Smith deliver a speech to garner support for his Design and Prospectus for a National Gallery of History of Art at Washington.

Smith gratefully accepted, and the firm of Renwick, Aspinwall & Russell spent six months completing their contribution.

[9] In 1861 Auchmuty withdrew to serve in the army during the American Civil War, and the firm was shortened to Renwick & Sands.

[12] One of the last major works completed by the firm during the elder Renwick's lifetime was the George Walter Vincent Smith Art Museum in Springfield, Massachusetts, dedicated about two months before his death.